How Much Water Can I Change At One Time?

[Scott MacAdam]

MY water in my 25 gallon is GROSS. it's really murky and disigusting and i feel bad for the fish in there because i have not come up with a plan yet as to what to do. i think doing a big water change would help the water condition but not sure if it would make the fish in any better of a situation. My uncle has tested my water(because he also has fish and he lives across the road) , and he told me the water had perfect stats for most tropical fish(i'm on a well system way out in the sticks). So this may help if i can do a large change all at once. i've tried adding the "water clear" stuff and it did nothing, it's supposed to take out cloudyness and such so i figured it would work, but nothing.

how much can I change at once percent wize without putting my fish in danger?

and how often ?

thanks alot .

 

[tttnjfttt]

General rule is no mroe than 25% at one time. How are your fish acting? Do they seem bothered by this? If not, i wouldn't be too worried about doing large changes, as they are very stressful.

By murky water do you mean cloudy looking?

 

[steelhealr]

I"ve been doing 30% water changes for months....have seen no ill effects. SH

 

[fishing4exotics]

In the past I done as much as a 100% water change using Prime by Seachem. It was a 180 gallon planted tank with 10 Tigrinus that had to be moved. But, if I had to change water on a tank that has not been changed in ages I would do 25% water changes everyday. Do this until you are satisfied with clarity of your tank. Then do a 25% water change on a weekly basis.

 

[Torrean]

It takes fish about 3 days to adjust to a new PH. What is the PH of your tank and what is the PH of your tap. if they are more than say .5-1 point apart I would do 25% water changes every 3 days. Really my advice is to do a 25% water change weekly until it clears up. If the fish aren't sick or distressed then going slowly would be best

 

[thefishykid]

i have tropical fresh water and i have done 30% water changes since i had the tank on a weekly basis. also when you clean out your filter use some of the water from your tank as this keeps vital bacteria in the filter that your tank needs. my tank has been running for just over 2 years and have had no problems i have heard people doing 50% water changes in more drastic sircumstances till they are happy that the tank is ok but have never done this myself so dont know hoope this helps you out a bit

 

[Bignose]

It takes fish about 3 days to adjust to a new PH.

That doesn't seem anywhere near right to me, so I'm gonna have to ask you for a source on that.

Here's why it doesn't seem right to me. In nature, lakes and ponds' pH changes a lot, from day to day, even during the day. In Diana Walstad's book Ecology of the Planted Aquarium there is a graph of a lake's pH taken every hour throughout a day and the pH changes like 1.2 units throughout the day (I'm moving so that book is packed away at the moment and I can't look it up). One day, not three. Not only that, but imagine a fish in the acidic Amazon basin when it starts raining, the rainwater washing in off the ground is not acidic (the acid comes form the decaying vegitation in the river). The pH in the rivers change pretty quickly, yet those fish survive.

The reason pH is important in this question is we need to know if the tank is cycled in anyway. If the tank has not has its water changes in a long time the water, there is probably ammonia and the water is very acidic. If the water is acidic, it is protecting the fish from the ammonia, since at low pHs the ammonia-ammonium equilibrium is shifted toward ammonium, much less deadly to the fish. If you start replacing that water with newer, higher pH water out of the tap, you will dilute the ammonia, but you will also shift the equilibrium back towards ammonia which could then kill your fish.

So, the water needs to be changed, but slowly. I would like 5% every few hours. Go as slow as your patience can handle. If you don't have test kits, take a water sample to your LFS where they will most likely test it for free. Take also a sample of your tap water that has sat out a few hours (you want the water to sit out a few hours so that any dissolved gases in your tap escape and we get the true values of the water you will be putting in your tank).

Finally, if the pH of the tank is the same as your tap, and there is no ammonia or nitrite, you can do alrge changes. But, I suspect that there is ammonia and low pH in your tank, so again I recommend very small, very frequent changes.

 

[Torrean]

Can't give you the source right now. I'm not positive because it's been several months since i've read it but I believe I got that information from a book that my sister has about aquarium fish. I will try to get the title as soon as I can but a direct quote will take a little longer. Please PM me if in a week I have not responded because it means I have forgotten. I thought that it was odd that it would take that long for a fish to acclimate too since most acclimation methods involve mixing the water over an hour or two but that's what the book said. I will take another look as soon as I can manage. Like I said if it goes more than a week or so then please PM me. I want to sort this out pretty badly. And if I am wrong (which is very possible) or the book is wrong (which is a little less likely but still entirely possible) I thank you for educating me.

 

[Bignose]

Here's a little more to mull over, Torrean: According to Evans, Piermarini, and Choe "The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste" Physiology Review 2005, the return of blood towards the control pH is primarily due to adjustments of blood bicarbonate concentrations via exchange of acid-base equivalents at the gills. Over 90
% of the action occurs at the gills.

Basically, what is boils down to is that the fish exchanges CO2, Na+, and Cl- at the gills until the pH balance between the water and their internals is just the way they want it. Another quote from the above article: "Although variable with the type and extent of the acid-base disturbance, compensatory transport is usually activated within 20-30 min of the disturbance and can reach net-acid or net-base excretion rates of 1,000 micromol per kg per hour."

If I just let the flux rate be 100 micromol per kg per hour, I think that that means that the fish can change its internal pH around 4 units per hour per kg of the fish or faster down to a pH of 4.0 (after that the time starts increasing exponentially, i.e. 10 hours to get down to 3.0) I actually don't know what the internal pH of a fish is... anyone?. So, smaller fish (smaller kg) can change their pH faster -- makes sense, smaller circulatory system, easy to change concentrations in a smaller volume.

What is really interesting is that the acid-base exchange rate is also dependent upon the salt (Na+ and Cl-) solution, so GH and KH play a much larger role than may be usually suspected. This thread http/www.fishforums.net/index.php?showtopic=123070 started just the other day linked to a site whose author deduced this relationship from experience.

So, it appears if the salts in the water are favorable, most aquarium fish can adapt to a change in pH pretty quickly -- in a matter of minutes really. But, if the changes in salt and total dissolved solids are big, the fish may not be able to use its ability to adjust its pH and that causes shock. In a funny analogy, a change in TDS is to fish's ability to change its pH like kryptonite is to Superman's super strength.

 

[Torrean]

WOW ... I almost understand all of that.

first. So fish breath, drink, adjust internal PH, and urinate through there gills...very interesting stuff.

Secondly what is a micromol? Just a very small unit of measure?

Third. In your example you reduced the ratio by a factor of 10 (1000-100) right? Or did you just say that because in the quote it says it CAN reach a rate of 1000 ( in optimal TDS conditions). I'd guess the internal PH of a given fish would be relative. It changes with the water it's in. I believe the correct question would be what is the natural PH of a fish in the wild. Then you try to match that. Or just let the fish adjust to your PH.

fourth. When you talk about the fish changeing it's internal PH by four points are you saying that a 1 kg fish can go from a PH of 8 to a PH of 6 in 30 min (after the 30 min waiting period)?

fifth. if the salt content in the water is high then it will take longer for the fish to adjust because they adjust by releasing salts and there are already a lot of salts in the water. This prevents quick diffusion. But if the salts are low then the fish will diffuse salts into the water quickly causing a quicker adjustment. I'm a little confused about this part. Is it about the change in TDS that controls the speed of flux or is it simply the TDS content of the tank they are in when the PH changes?

thanks for the links I'll take a look at them. I'm a little intimidated but I'll take a look.

 

[thapsus]

I change 50% or more of water weekly.

 

[juliehainsworth]

I do a 25% water change daily and occassionally do 30% water change but thats only because my tank is over populated!

Have also done a 100% water change (once) kept all the fish in a bucket for 3days whilst I did that with a heater and airstone! Think I did the wrong thing at the time as the heater some how ended up on top of a khuli loach and it ended up with a curved spine but lived for a further two years after! Wouldnt recomend doing it though! I was lucky that my fish all survived it but felt bad after!

 

[Bignose]

One mole (abbreviated mol) is 6x10^23 molecules of the same molecules. Why do chemists use number instead of mass? That way chemical equations like 2 H2 + O2 --> 2 H2O make sense. 2 H2 molecules combines with 1 O2 molecule to make 2 molecules of water. You can use the molecular mass (traditionally known a molecular weight) to calculate how much mass is in one mole of a molecule. e.g. water is H2O which is about (2*1 + 16 = 18) (yes, there is some decimals in there, but I don't want to look it up at the moment). That means 6x10^23 molecules of water has a mass of 18 g.

One micromol is 10^-6 of a mol.

Yes, I took 1/10th of the maximum rate as a reasonable estimate. But, remember that the pH scale is logarithmic, so assuming that my estimate is right (which I am pretty unsure about) it won't take 30 mins to go from any two pH units. But, it would take an hour to go from any higher pH down to 4.

The reason it isn't a half hour to go 2 pH units is due to the definition of pH

pH = -log(base 10) of the concentration of H+ ions. so if the pH is 7 the concentration is 10^-7 mol H+/L.

If you can adjust 10^-4 mol H+/L per hour, at time 0 the concentration is 0.000 000 1, and after one hour it is 0.000 100 1. If it was completely constant, after 100th of an hour (40 or so seconds) it would be 0.000 001 1, or about a pH of 6 after just 40 seconds. Looks like it would be about a pH of 5 at about 6 or 7 minutes. The rest of the hour is taken to get to a pH of 4. But all that hinges on a lot of things, like constant excretion rate (unlikely), concentration in the fish is uniform (more unlikely), many more things that I am sure I am not taking into account.

I also don't know in what way the salt content affects the rate, I just know it was stressed that the salt content is important for pH adjustment. This is going to require a lot more looking things up that I may not have the time to do right now. I'm not even sure my school library has the books/articles I'd need to see to be sure about anything.

 

[Torrean]

thank you for the time and thought that took. I'll need a few days of rereading it to understand it LOL but thank you very much