Does It Need To Be Changed So Often?

[andywg]

I agree with what you say Andy, but i think the point is that in the average home FW aquaria, which usually lacks fluidised bed filters and laboratory grade testing equipment, we do the best we can.

And the studies intimate that fluidised bed filters are not necessary. And why need laboratory grade test equipment? Why not just do water changes based on nitrate accumulation?

I agree that water changes aren't necessarily required every week, or even every month perhaps, but where is the line drawn?

See above.

MW often advises newbies on TFF (as do I) and rather than putting them off fishkeeping for life by telling them that they might not need to do water changes but if they do we're not sure how much or how often, we stick to the easier option, weekly water changes. Safe and easy, which is what most hobbyists (especially beginners) want!

That side is not the problem. My problem is when someone asks and says "My water stats are fine, even after a week my nitrates have barely gone up, do I need to do a water change" and everyone states that they must, when it just isn't true.

Dave and rabbut,

Just wanted to mention that while it is true about the population biology studies, my speculations about "fry school hormones" was just that, pure speculation - just thinking from the assumption that what rabbut said was something known by breeders and really exists. I wouldn't be surprised of its existance and I wouldn't be surprised if once again there is no science to really help us out with it...

~~waterdrop~~

I am fairly sure I have read discussions of a hormone which does inhibit growth in the two ichthyological texts I have. It wouldn't work very well, as Dave has said, in a fast flowing stream, but in the Amazon where vast areas can become landlocked into smaller puddles it could prevent fish outgrowing the available food.

Fish growth rate is affected by a myriad different factors and there is quite some discussion on it.

 

[Miss Wiggle]

Safe and easy, which is what most hobbyists (especially beginners) want!

I agree with you BTT.

I accept your points Andy, as you know I'm not that scientifically minded and don't for a minute think I could win this argument with you.

However all I'll say is this.

The response I give to questions will vary depending on who posted them and where they posted them. The vast majroity of people who post in the new to the hobby forum are just starting out, while we get a handful who want to delve into the sciency stuff, there are also a lot of them who are confused enough as it is with the nitrogen cycle to learn. I try to steer advice in this forum more towards sensible practical advice which will get the majority of home systems running smoothly. We all know there is more than one way to run a tank sucessfully and we know a lot of factors will influence what is a suitable choice for each individual circumstance.

So yes my advice in the forum may be run of the mill stuff, I'm not pushing boundaries or anything. But I'm trying to get people off the ground with what can be a confusing hobby. I think we should sometimes exercise caution when bandying round advice based on experimental stuff when we're talking to people who may not have the basics covered yet. Yes we should encourage people to learn, but we should also make sure they walk before they try to run.

 

[backtotropical]

Why not just do water changes based on nitrate accumulation?

I wouldn't recommend water changes based solely on nitrate accumulation because there are a whole lot more factors than nitrate which water changes deal with. Replacing required mineral content and keeping kH steadily topped up to avoid pH crashes are just the tip of the iceberg. There are also air-bourne pollutants which we are unable to test for with proprietary aquarium test kits, hence why i said you would need lab-grade equipment to carry out the experiment properly. A nitrate test kit could tell you everything is fine, when the overall picture could be quite different.

Also, for example in planted tanks, nitrate may never rise. Does that mean a water change is never required to keep all the inhabitants healthy? I'm unconvinced.

My problem is when someone asks and says "My water stats are fine, even after a week my nitrates have barely gone up, do I need to do a water change" and everyone states that they must, when it just isn't true.

I disagree. It may not be true, and that uncertainty is a key factor here, but as we have already said, it depends on individual circumstances, nitrate level, kH level, TDS, air-bourne pollutants etc etc. In the absence of all the required info (especially the ones we can't test for), surely water changes are the best policy? Prevention is better than cure, so to speak.

I know that my tank may be ok without water changes, but i am not willing to risk it.

 

[Corleone]

An addition to what BTT said: Water changes are cheaper than anything else you can do to the tank. It'd cost me less than two dollars on my water bill to do 100% water changes on both my tanks, fill up the leaky 50 gallon in my garage, and set up my quarantine tank. If I skip water changes and lose my least expensive fish, I'm out more than that when you figure gas to drive to the store, and a run of medicine will start around $5 and could run me $50 if I have to treat my entire 55 gallon tank.

 

[tenohfive]

Whoa, whoa, whoa. If theres going to be an in depth discussion, please move it to the scientific section - NOT the New to the hobby forum, where someone flicking through for advice on setting up a new tank could read a line that stands out (such as "Indeed, I recall that there was certainly nothing found to suggest that water changes must be done every week.")

People who are new to the hobby should be doing regular water changes. Those who know alot more, and have a lot of experience can take there own calculated risks. Thats fine, but please stop posting such theories in this forum - it is not the place for it. Its a place for beginners advice, and this can only lead to confusion.

 

[rabbut]

Whoa, whoa, whoa. If theres going to be an in depth discussion, please move it to the scientific section - NOT the New to the hobby forum, where someone flicking through for advice on setting up a new tank could read a line that stands out (such as "Indeed, I recall that there was certainly nothing found to suggest that water changes must be done every week.")

People who are new to the hobby should be doing regular water changes. Those who know alot more, and have a lot of experience can take there own calculated risks. Thats fine, but please stop posting such theories in this forum - it is not the place for it. Its a place for beginners advice, and this can only lead to confusion.

Perhapse we could shift the the scientific section, unless the OP objects?

Dave and rabbut,

Just wanted to mention that while it is true about the population biology studies, my speculations about "fry school hormones" was just that, pure speculation - just thinking from the assumption that what rabbut said was something known by breeders and really exists. I wouldn't be surprised of its existance and I wouldn't be surprised if once again there is no science to really help us out with it...

~~waterdrop~~

I have seen first hand that more water changes seems to equate to quicker growth rates, so I'm sticking by my guns in the advise to the OP to keep up with good waterchanges. I remember reading a few linked to papers about the effects of growth hormones many eons ago over in tropical discussion (i.e. pre. waterdrops arival and pre. scientific section) I cannot remember the papers in detail, and thus I'm not very well read in this topic, so I can't realy debate with andywg here....

In puddles, as Andy says, hormones can build-up. In effect, out tanks are glamorised puddles, so they can build-up in our tanks also. hormones in streams will be washed down-stream, so I suppose they could be presant in sufficiently high ammounts at the end of a water caurse also. At the top of a stream, I doubt they would have any effect though...

Just my 2 cents worth.
Rabbut

 

[andywg]

So yes my advice in the forum may be run of the mill stuff, I'm not pushing boundaries or anything. But I'm trying to get people off the ground with what can be a confusing hobby. I think we should sometimes exercise caution when bandying round advice based on experimental stuff when we're talking to people who may not have the basics covered yet. Yes we should encourage people to learn, but we should also make sure they walk before they try to run.

BUT

I return to my point above, this person asked if they must do water changes when nitrates are not going up. The simple answer is that water changes at x% per y days are simply not necessary and they do not have to do so.

This thread is not someone asking about what a water change is or how to do one, but rather asking a specific question about whether water changes are necessary when the water quality is still good. Do you still believe that in such circumstances we should trot out the simple easy to understand FAQ stuff, or actually engage our grey matter and provide all the information out there for the OP to decide which way they want to go?

I wouldn't recommend water changes based solely on nitrate accumulation because there are a whole lot more factors than nitrate which water changes deal with. Replacing required mineral content and keeping kH steadily topped up to avoid pH crashes are just the tip of the iceberg. There are also air-bourne pollutants which we are unable to test for with proprietary aquarium test kits, hence why i said you would need lab-grade equipment to carry out the experiment properly. A nitrate test kit could tell you everything is fine, when the overall picture could be quite different.

And the science posted in the thread above shows that it is of such a negligible amount that it seems to have no effect on fish over 300 days, so over a month or so it will not be a problem. Thus, a weekly water change when nitrates are not rising will not be causing a sudden drop in KH as the drop in KH is as a result of the nitrogen cycle.

Also, for example in planted tanks, nitrate may never rise. Does that mean a water change is never required to keep all the inhabitants healthy? I'm unconvinced.

Perhaps you should read Diana Walsted's book on keeping more natural aquaria where she advocates no water changes for at least 6 months as well as no filters in planted tanks. You may not be convinced, but there is plenty of evidence out there to support other ways of doing this.

I disagree. It may not be true, and that uncertainty is a key factor here, but as we have already said, it depends on individual circumstances, nitrate level, kH level, TDS, air-bourne pollutants etc etc. In the absence of all the required info (especially the ones we can't test for), surely water changes are the best policy? Prevention is better than cure, so to speak.

Water changes may or may not be the best policy. As I have noted above, the things you list are not shown to build up to anything like dangerous levels over short and mid term periods (of say up to a month). Why waste energy on clean water when it isn't required?

The simple fact is that while water changes do not do any harm, no one can show any actual evidence of a lack of water changes over a couple of weeks in a tank where nitrates rise slowly causing problems. So, if someone says that their nitrates don't rise over a week should they do one every week, why not advise dropping the frequency to once a fortnight or once a month?

I know that my tank may be ok without water changes, but i am not willing to risk it.

But this was not about your tank, rather it was about the OP's tank where the nitrates do not rise enough to warrant a water change on their own within a week.

Whoa, whoa, whoa. If theres going to be an in depth discussion, please move it to the scientific section - NOT the New to the hobby forum, where someone flicking through for advice on setting up a new tank could read a line that stands out (such as "Indeed, I recall that there was certainly nothing found to suggest that water changes must be done every week.")

Yeah, let's not have completely correct information when we can just feed half truths to keep it simple. Tell you what, how about we add a line that a fish's organs keep growing even if their skin and skeleton stop growing due to being kept in too small a tank and that eventually a fish will die from the organs popping out. It's completely fabricated, but it will stop new aquarists from keeping too large a fish in a small tank.

Or we could strive to be accurate and correct throughout the forum and incorporate more than just one accepted way of doing things. Guess which I prefer.

Oh, and just who gets to decide on what is the correct way to do things that we must all adhere to in the newbie section?

People who are new to the hobby should be doing regular water changes. Those who know alot more, and have a lot of experience can take there own calculated risks. Thats fine, but please stop posting such theories in this forum - it is not the place for it. Its a place for beginners advice, and this can only lead to confusion.

Why yes. How dare I post suggestions that there are different ways of keeping fish that are equally successful!

If it's all the same to you, I will post advice on keeping fish how I see fit where I see fit. I will not start curtailing correct information just because it may confuse someone to read something that is not the accepted norm of the forum.

 

[backtotropical]

And the science posted in the thread above shows that it is of such a negligible amount that it seems to have no effect on fish over 300 days, so over a month or so it will not be a problem.

I don't see anywhere in that science where it takes into account the air-bourne pollutants in the average home. As i said above, these seem to be the real danger as the average aquarist can't test for them, and we therefore don't know how much (or even what) has found its way into the tank water.

I quote Bignose's post from the same thread you linked to, and in particular the last three sentences

Secondly, there are all manner of chemicals that get into the water. I'm talking carpet fumes, oils in the air from cooking, cleaners, cigarette smoke (if you smoke), fumes from candles or air fresheners, etc. etc. Again, for us, we just need to open the window or run an exhaust fan over the stove to refresh our environment. The amounts of these things in the tank are small, parts per million, parts per billion, maybe even parts per trillion. But, low level long-term exposure to chemicals can be just as bad as acute exposure to high levels. Water changes dilute these out and removes them.

In the absence of a way for the average aquarist to test for these pollutants, water changes (even if nitrate is not rising) are a good preventative measure. Can we have too much prevention?

Perhaps you should read Diana Walsted's book on keeping more natural aquaria where she advocates no water changes for at least 6 months as well as no filters in planted tanks. You may not be convinced, but there is plenty of evidence out there to support other ways of doing this.

Yes, i have the book, and i have nowhere said that there aren't alternative ways of doing it, only defended the way which you are trying to deem 'unnecessary'. I also believe that some of her theories are now thought to be incorrect, Alleopathy being the one which immediately springs to mind.

Water changes may or may not be the best policy.

My point exactly, so why take the risk of not doing them, especially when the only scientific evidence available to us only covers some of the bases?

So, if someone says that their nitrates don't rise over a week should they do one every week, why not advise dropping the frequency to once a fortnight or once a month?

Simply because monthly water changes may be fine for one tank but not another, and newbies need to walk before they can run. Why advise to cut back the perventative measures we take to keep our fish healthy, and how far do you go with it? You could say monthly changes, but this again would be a time frame plucked from nowhere in particular, and may or may not be necessary. Would you advise a newbie to cut back water changes as far as possible until fish start dying, then they know where the boundary is?

If it's all the same to you, I will post advice on keeping fish how I see fit where I see fit.

I suppose that is the conversation closed then, as the same applies to everyone else posting here, including those advocating weekly water changes as best practice? Conclusion Everyone is entitled to their opinion?

 

[andywg]

I don't see anywhere in that science where it takes into account the air-bourne pollutants in the average home. As i said above, these seem to be the real danger as the average aquarist can't test for them, and we therefore don't know how much (or even what) has found its way into the tank water.

OK then, if you think these things may cause an issue, show me some evidence where these are an issue. If you are saying we should do water changes because of air-borne pollutants, show me exactly where you are getting information that they build up to problematic levels within a month.c

In the absence of a way for the average aquarist to test for these pollutants, water changes (even if nitrate is not rising) are a good preventative measure. Can we have too much prevention?

You will also note that bignose could not say that these things would become a problem. He was musing over what may or may not be a problem when present in tiny levels. I repeat from above, show me some evidence that air-borne domestic pollutants will become a problem within a month (or any time period), then I shall say we should all do water changes more often.

My point exactly, so why take the risk of not doing them, especially when the only scientific evidence available to us only covers some of the bases?

Because there is no risk shown. Did people used to do water changes every week? No. Do all the fish die? No. There are more ways to keep fish than the FAQ says, just because someone is posting in the newbie thread does not mean we can't give them all the information and let them make their own informed decision.

If you think there is a risk, show me some evidence of where not changing a system with no appreciable nitrate accumulation every week has caused issues.

Simply because monthly water changes may be fine for one tank but not another, and newbies need to walk before they can run. Why advise to cut back the perventative measures we take to keep our fish healthy, and how far do you go with it? You could say monthly changes, but this again would be a time frame plucked from nowhere in particular, and may or may not be necessary. Would you advise a newbie to cut back water changes as far as possible until fish start dying, then they know where the boundary is?

No, I would say cut it back until the nitrates are at a marked difference from the tap water. Is that such a ridiculous concept?

And you are right, my monthly figure is drawn out of the air, just like weekly water changes. It should be done by monitoring pH, KH and nitrates, but somehow most end up doing them weekly; probably because most people have a mostly weekly schedule to their lives.

If it's all the same to you, I will post advice on keeping fish how I see fit where I see fit.

I suppose that is the conversation closed then, as the same applies to everyone else posting here, including those advocating weekly water changes as best practice?

Not really. If you actually read my post it was to someone indicating that this conversation should stop because it is in depth and some newbie people might not read all if the thread. I prefer not to have the newbie section as some ring fenced area where we can't discuss anything that might go against what is written in the FAQs and where we can still challenge the information presented.

To recap, you have still given no reason why someone must do water changes every week when nitrates are not rising other than some unknown possible risk of domestic air-borne pollution. If these were really such a risk, do you not think that the more delicate subjects kept in reef tanks would have problems from the water therein being changed at a rate of once per fortnight or once per month as is often the case?

Again, return to the OP, this was not someone asking what a water change is or how to do one, but a particular question on whether one must do one even when the stats show you don't need one. The simple answer to that is no. I can think of no system that will need water changes every week that will not also have rising levels of nirates with it.

Most systems do have rising levels of nitrates between water changes, so water changes every week are more appropriate, however one size does not fit all and if the tank doesn't need a water change, why should we tell people they must do so?

 

[backtotropical]

OK then, if you think these things may cause an issue, show me some evidence where these are an issue.

I have no evidence to suggest that these pollutants are an issue, just as you have no evidence to show that they are not a problem. Because there is no existing scientific papers which prove one way or another, doesn't mean the threat doesn't exist. IMO it almost certainly does.

show me some evidence that air-borne domestic pollutants will become a problem within a month (or any time period), then I shall say we should all do water changes more often.

I am not asking you to conform to a weekly water change regime. I merely think that it is a good starting point for beginners.

No, I would say cut it back until the nitrates are at a marked difference from the tap water. Is that such a ridiculous concept?

Not at all, and it is what i personally have recommended to many members on TFF when it appears appropriate, if you care to look through my previous posts. The air-bourne pollutants, as Bignose says, probably linger in very small quantities in most tanks (although it absolutely differs from tank to tank depending on circumstances), and basing water changes on nitrate accumulation is probably sufficient for most tanks but there are always exceptions, for example tanks with very soft water will be more susceptible to problems when nitrate levels are low than tanks with hard water would be.

The fact remains that your methods are feasible as are the weekly water change methods, but beginners who barely understand what the nitrogen cycle is need clear simple advice. We could advise them of the facts and suggest that they base their water change schedule on the pH, hardness and nitrate accumulation in their tank, but most wouldn't understand. We would be providing the facts, but they would be, in essence, useless to the poster requesting advice.

There are more ways to keep fish than the FAQ says

You seem to keep coming back to this, and i will say again for the record that i have never suggested otherwise.

just because someone is posting in the newbie thread does not mean we can't give them all the information and let them make their own informed decision.

I'm not suggesting that you shouldn't post 'all the information' in the newbie section, simply that it isn't always appropriate to the situation. 'All the information' is excellent if the recipient can understand and use it, but unfortunately useless if they can't.

somehow most end up doing them weekly; probably because most people have a mostly weekly schedule to their lives.

Again, exactly my point, and probably the reason that the weekly water change regime was invented in the first instance.

If these were really such a risk, do you not think that the more delicate subjects kept in reef tanks would have problems from the water therein being changed at a rate of once per fortnight or once per month as is often the case?

Maybe so, but do you have any evidence to suggest that this is not the case? Again, i doubt it. How many unexplained deaths occur in these tanks?

Most systems do have rising levels of nitrates between water changes, so water changes every week are more appropriate, however one size does not fit all and if the tank doesn't need a water change, why should we tell people they must do so?

Again, i have never suggested that weekly water changes are 'necessary', only that it is good practice as a preventative measure against potential problems.

To conclude, your advice is sound Andy, and can be well utilised by more experienced aquarists. IMO, a more simplistic approach appears to work better with 'newbies' who maybe don't have the knowledge and experience to use your advice to its full potential, and hence the weekly water change recommendation appears.

 

[andywg]

I have no evidence to suggest that these pollutants are an issue, just as you have no evidence to show that they are not a problem. Because there is no existing scientific papers which prove one way or another, doesn't mean the threat doesn't exist. IMO it almost certainly does.

So you are basing your water change regime advice on potential risks which you can provide absolutely no evidence for, but merely because someone has suggested they could be an issue at some point and you like that idea.

I am not asking you to conform to a weekly water change regime. I merely think that it is a good starting point for beginners.

Indeed, but this thread is not about giving a starting point for beginners. It is about whether one can leave water changes longer in a lighter stocked tank that does not have nitrate accumulation. The simple answer is yes.

Not at all, and it is what i personally have recommended to many members on TFF when it appears appropriate, if you care to look through my previous posts. The air-bourne pollutants, as Bignose says, probably linger in very small quantities in most tanks (although it absolutely differs from tank to tank depending on circumstances), and basing water changes on nitrate accumulation is probably sufficient for most tanks

So we don't need weekly water changes for all then. I'm glad we are all agreed that weekly water changes are not an absolute.

but there are always exceptions, for example tanks with very soft water will be more susceptible to problems when nitrate levels are low than tanks with hard water would be.

But it is still based on nitrate accumulation.

The fact remains that your methods are feasible as are the weekly water change methods, but beginners who barely understand what the nitrogen cycle is need clear simple advice. We could advise them of the facts and suggest that they base their water change schedule on the pH, hardness and nitrate accumulation in their tank, but most wouldn't understand. We would be providing the facts, but they would be, in essence, useless to the poster requesting advice.

And putting the facts and adding "A common fall back is to just change water every week to be on the safe side" is too hard? And who are we to decide at what point someone can or cannot understand the idea that if nitrates drift up or pH/KH drifts down they should change water. That's hardly rocket science. The only reason they could not understand that would be if they didn't understand testing, but we are all for testing from all new members.

I'm not suggesting that you shouldn't post 'all the information' in the newbie section, simply that it isn't always appropriate to the situation. 'All the information' is excellent if the recipient can understand and use it, but unfortunately useless if they can't.

And if you decide someone can't understand it we should drop back to the FAQ, yes? Again, how do we decided if someone can or cannot understand the information without putting it there for them?

Maybe so, but do you have any evidence to suggest that this is not the case? Again, i doubt it. How many unexplained deaths occur in these tanks?

One cannot prove a negative, but merely show that there are no indications that it is the case. I say again, SPS corals are massively more sensitive to their water conditions than fish, one only needs to look at the low levels required in acro farm tanks to see that. Even these sensitive creatures have no issue with the air borne pollutants building up in the tank over anything from 2 weeks to a year and more (a number of reefers change as little water as possible).

My suggestion is that if such pollutants were really a problem as you say we would not see successful reef tanks with fortnightly and monthly water changes (often as little as 10% or under even then).

So, while there is no evidence either way on the pollutants, I can show you why they do not appear to have any affect. There can be little doubt that on the balance of probabilities, air borne pollutants are not an issue in tanks for some time, if at all.

Again, i have never suggested that weekly water changes are 'necessary', only that it is good practice as a preventative measure against potential problems.

That is fine then. We are agreed that the simple answer to the OP's question is that they do not have to do water changes every week.

To conclude, your advice is sound Andy, and can be well utilised by more experienced aquarists. IMO, a more simplistic approach appears to work better with 'newbies' who maybe don't have the knowledge and experience to use your advice to its full potential, and hence the weekly water change recommendation appears.

So at what stage do you feel a newbie becomes experienced enough to be told they don't have to do a water change every week? Will it be a matter of time spent in the hobby, a number of tanks or maybe a set number of fish kept?

That is not for me. Put all the information out there and invite them to ask questions. I hate assuming that someone cannot understand something just because they are new, and if we don't tell the new people all the facts, how will they learn them?

 

[backtotropical]

So you are basing your water change regime advice on potential risks which you can provide absolutely no evidence for, but merely because someone has suggested they could be an issue at some point and you like that idea.

No. I base my advice on the obvious fact that most, if not all, households will have some form of air-bourne pollutant which can be readily taken on by the water in a fish tank and which can potentially be deadly to fish. Slightly different to what you are suggesting.

It is about whether one can leave water changes longer in a lighter stocked tank that does not have nitrate accumulation. The simple answer is yes.

Agreed, but the not so simple question is how long is it safe to leave it. It appears that neither you or I have the answer, so most people base the water change interval on personal preference and what they believe to be correct. There is no definitive answer, and everyone's regime is different.

So we don't need weekly water changes for all then. I'm glad we are all agreed that weekly water changes are not an absolute.

Absolutely, and i never suggested that weekly water changes are an absolute. I'm unsure who you appear to be arguing with on that point.

But it is still based on nitrate accumulation.

And other things. As i've said already, nitrate accumulation is not the only factor which needs taken into account. There are several others.

And putting the facts and adding "A common fall back is to just change water every week to be on the safe side" is too hard?

Not at all, and nobody is asking you not to. On the other side of the coin, is just advising weekly water changes so wrong?

And if you decide someone can't understand it we should drop back to the FAQ, yes? Again, how do we decided if someone can or cannot understand the information without putting it there for them?

You use your judgement Andy. Sometimes you get it right, sometimes you get it wrong. Its called human nature.

So, while there is no evidence either way on the pollutants, I can show you why they do not appear to have any affect.

And how do you do that? What do you attribute unexplained losses to in these tanks? I assume it could be any number of things, but definitely not air-bourne pollutants?

My suggestion is that if such pollutants were really a problem as you say we would not see successful reef tanks with fortnightly and monthly water changes (often as little as 10% or under even then).

As i have maintained all through this discussion, it depends on individual circumstances. It is ridiculous to suggest that nobody would be successful if air-bourne pollutants can be a problem. Of course some people would be successful, and others would be unsuccessful and probably unable to attribute a cause to their demise, as is the case.

That is fine then. We are agreed that the simple answer to the OP's question is that they do not have to do water changes every week.

Yes in general, but not specifically. The OP is referring to the fry tank and as Rabbut points out, the hormone build up in these tanks is said to cause problems, so in this particular case, weekly water changes could even be considered insufficient.

So at what stage do you feel a newbie becomes experienced enough to be told they don't have to do a water change every week? Will it be a matter of time spent in the hobby, a number of tanks or maybe a set number of fish kept?

That is not for me. Put all the information out there and invite them to ask questions. I hate assuming that someone cannot understand something just because they are new, and if we don't tell the new people all the facts, how will they learn them?

Its often quite obvious roughly how much knowledge someone has. If someone asks "What is cycling?", it's probably safe to assume that they don't know much about nitrate accumulation. Again, its just a judgement call. We all do it whether you like it or not.

In an ideal world i wouldn't like the idea of assuming someone won't understand either, but in the real world, not all hobbyists are even interested in learning about water parameters and genuinely just want to know should i perform water changes, and usually the best advice is yes. Generally speaking, if someone is interested and wants to find out more on why they should or shouldn't do a water change, they will ask. That would be the point where i would offer more detailed information.

I feel this discussion isn't really producing anything new or useful anymore, but instead going round in circles and pedantry seems to be creeping in, in places. I feel that i have outlined my thoughts on the matter clearly, and this could go on forever, should i allow it to. With that in mind, to hopefully conclude my input to this thread, my advice to the OP is this

Weekly water changes won't do any harm (and may bring substantial benefit) so long as you match the pH, hardness and temperature and properly dechlorinate the water. The very fact that you are already performing weekly water changes will virtually eliminate the need to worry about pH or hardness as these will be kept relatively constant by the frequent replenishment of water. The only thing you really need to consider therefore are matching temperature (which only needs done very roughly) and properly dechlorinating the water which i assume you already do?

Changing the water weekly is a good preventative measure against various things which can be detrimental to the health of your fish, so is a good starting point.

If your stats are perfect and no nitrate has accumulated since the last water change, a water change probably isn't "necessary" as such, but i feel that it is best practice to do so anyway for several reasons which you will have read above.

If you want to experiment with lowering the volume or frequency of your water changes, then nitrate accumulation is a good guide, but only a guide and by no means conclusive.

That said, the tank in question houses fry which is different altogether. Rabbut's advice on this point should be considered carefully, and you may even wish to consider increasing the frequency of your water changes on this basis.

Hope this helps.

BTT