i have two tanks set up.
in my 180L i do a water change weekly of around 25%.
but my fry tank (54L) water is crystal clear, stats are all brilliant, do i need to do weekly changes in this tank or could this one be left a little longer?

Hi Spishkey,

I personally do water changes just to change the water. Just because the water stats are ok you should still do weekly water changes.

It is so easy to fall into a rutt by putting of a water change.

In your fry tank it should only take 10 mintues. If I had 2 takes i'd do them at the same time.

Martyn

there's a thread over in the scientific section which discusses why you should still do water changes even if your stats are perfect

With fry its advisable to do larger and more frequent waterchanges, as they are more prone to stunting due to growth horemone build-up, that we can't test for. Some breeders do 90% daily to get good growth rates... Fry tanks are usualy very heavily stocked though. If you have about say 30 fry in a 30g, I'd do 2 50% changes a week personally, but any higher and I'd consider 50% either daily or every ohter day as minimum, untill they reach 1/3 of their adult lengh, and them I'd steap back to 25% as often. At 1/2 adult lenght, go to 50% weekly, and as of 3/4 full size, normal 25% weekly, unless heavily stocked, and then do more changes, or larger ones

All the best
Rabbut

^^rabbut, how very interesting! I've not heard of that.. (fry school hormones) I know that at Harvard and other places they've done years of studies in population biology to work out how animal populations have various methods, both common and unusual, to preserve the genes of the population as opposed to a particular individual of the population. Sounds like another of those sorts of things.. If the school of fry get too closely packed in then that could mean starvation or other peril to the entire school, so an anti-growth homone that has a stunting effect has an influence (and only under the close, packed in circumstances, how clever!) leading to smaller fish, leading to less stress on the food source, leading to possible survival of more of the gene pool...

Is this you're take on it?

~~waterdrop~~

Growth stunting due to hormone build up.....now there is something to be a little skeptical of. After all, how would this hypothesis stand up in a fast flowing stream where any hormonal build up is instantly washed downstream?

It reminds me a bit of Diana Walstad theorising over allelopathy in her book. This theory has now been largely dismissed due to its relative ease of testing by placing carbon in one tank to absorb the allelopathic chemicals, alongside another without carbon. Both tanks behaved the same.

In another test, several tanks were set up with a few hundred different types of plant in them. None of the tanks experienced any kind of algae bloom whatsoever. It is unlikely that all these plants were giving off the same allelopathic chemicals.

Is it not possible to run one tank of fry with a method that instantly removes any potential hormonal substances alongside one where they are allowed to build up?

Dave.

I personaly hadn't thought of that use for this growth hormone, so your take acctually explains a bit to me....Seems obvious now In the wild a dominat fish is usualy larger, adn thus the hormone doesn't effect it as much. It ensures that the dominant fish remains dominant I belive...
When I used to breed goldfish and livebares, I found that increased waterchange regime gave quicker growth rates and the fry didn't suffer stunting as freely...

It was just something I was chipping in from a few breeders I know, and also from personal expreience, as well as a few topics on stunting that I was reading a while ago, where some studies were investigating the effects of stunting and its caurses.

All the best
Rabbut

Edit to add after Dave's responce. You could set-up a tank running carbon in the filter and replace the carbon every 3-4days to remove growth hormones, and run another the same size with the same load of fry as the carbon filtered tank with the same waterchange regieme, and see what happens.

Further thoughts on stunting is that nitrate build-up is a contributor.

This post has been edited by rabbut: Jul 3 2008, 12:25 PM

Dont be led into a false security by your test kits.... they dont test for everything !!!!

Change that water.....

And were not studies found that showed one can create a closed loop system that doesn't require regular changes without impacting on the growth rate of tilapia?

Indeed, I recall that there was certainly nothing found to suggest that water changes must be done every week.

wow thank you all for the replies.


and some really amazingly intresting posts there! i never knew ll that! i shall now be doing 2 x water changes a week in the fry tank then! (is that enough? about 20 1-2 week old fry in a 60x30x30 tank?)


many thanks once again, i learn something new every day!!

Hi Andy,

I've always been one to feel in agreement with you that there are many, many paths to satisying and beautiful aquariums. Being one of the older guys, I can remember beautiful aquariums with slightly yellowed water in the 1960's where the aquarist was following the thinking of the day and hadn't changed the water in a long time. I don't know whether the fish lived shorter lives in those aquariums but at the time they usually seemed healthy to my untrained eye.

I hate to be just a parrot passing on advice that oversimplifies the bigger picture. With respect to water changes, at what point do you think, on average, that we might expect too much build-up of trace elements or organic substances in an average community tank? What kind of water changing pattern might we suggest to beginners that would help them develop a habit that would be healthy for the tank but would not be excessively fussy? Is a week unneccessarily too soon, is a month too late?

Personally, I don't have enough experience to offer a pattern that might be closer to having a real scientific basis. I went from my years of tanks when I was younger, where water change patterns were not a conscious thing to worry about (with consequent random behaviour on my part) to my recent few years where I've jumped to feeling quite positive about the usefulness of water changes for the healh of the tank.

~~waterdrop~~

haven't seen that study personally...... there's a whole world of a difference between a closed loop system and an average home aquarium though as well you know.

As I said, there's a thread discussing the various points in the scientific section.

It's in the thread you are talking about, it is discussed and quoted from by Spiderpig

The post is here. The study is Nadav Shnel a,b, Yoram Barak a, Tamir Ezer b, Zaev Dafni b,Jaap van Rijn a, Design and performance of a zero-discharge tilapia recirculating system Aquacultural Engineering 26 (2002) 191–203, and they said:

"The technical feasibility of zero-discharge recirculating systems incorporating denitrifiers fed with endogenous produced carbon has been studied by a number of investigators (Kaiser and Schmitz, 1988; van Rijn and Rivera, 1990; Schmitz- Schlang and Moskwa, 1992; Arbiv and van Rijn, 1994; Schuster and Steltz, 1998).
The latter studies were conducted during relatively short-term growth trials. In this study, we demonstrate that also on a long-term basis, fish can be successfully cultured without adverse effects associated with long-term use of re-use water. Although the system in this specific reported season included a fluidized bed reactor for nitrate removal, results of this study indicate that anoxic treatment might be accomplished successfully by eliminating this latter treatment step. Presently, the same tilapia culture system is operated successfully for the second successive year using a sedimentation/digestion basin as the only anoxic treatment stage."



Not massively. A closed loop system is one where there is not a constant refreshment of new water, that is the old water stays in the system. While the above is certainly larger than our aquaria, it is probably stocked on a similar enough level to draw parallels. Note that the growth rate is comparable ot other fish farms. Growth rate is dependant on many things, so keeping the growth rate up is a pretty good sign of decent water conditions.

Also remember this is talking about going for a year without a water change, rather than (say) a month.



And as I said, there was absolutely no science to support that one must change water every week in that thread. There was lots of musings over whether certain air-borne pollutants might cause issues, but nothing to suggest one must change water every week, or even every fortnight.

Consider reefs, often stocked with very sensitive invertebrates. These tanks are often changed once a fortnight or once a month. If an animal as sensitive as many of the Acropora spp corals are happy with such infrequent water changes, why wouldn't our comparatively hardy fish be?

If you want to do lots of water changes, go for it - they seldom do any harm. But I don't think someone should be told they should do water changes once a week if there is no need (which will depend on circumstances).

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.

I agree that water changes aren't necessarily required every week, or even every month perhaps, but where is the line drawn? I think the answer for most of us is that we just simply don't know (because it is too variable from tank to tank) and don't have the equipment required to find out without endangering the lives of our beloved pets, as each set up will be different. As you say, it depends on circumstances.

So in the absence of the detailed information required to determine whether our tanks and inhabitants will be fine with no water changes for 1 month, 1 year, 5 years, whatever, we stick to what we know, that water changes will almost always give us good water conditions.

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!

Cheers

BTT

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~~

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?



See above.



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.



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.