Tom: Per my original post, this is the SAME tank...the only difference is addition of CO2 to hold pH constant during refill. Overdose of CO2 I've seen/done...all fish at top of water gasping...pH below 6.5 or so. This is not the case here.
The practical:
So why have I never seen an issue for 2 decades?
Amano, most every nice scape you see, they do not adjust pH when they do water changes, they have so called sensitive species.
You are suggesting that this is an issue.
I'm asking and seeing if you really think it is............
I do not have to say what it may be that causing your fish issue.
All I'm saying is what it is not.
Also, do not believe everything you think, adding CO2 is rarely the only addition you have made, you might think that's the only parameter you have changed......but that is not for sure.
Whereas I've done this large water change and pH unit changes of 0.8 inside a few minutes with CO2 rich and tap water. Week after week, month after month, years after year after year.........MANY planted tank keepers have.
Now this is just the practical "does it make sense" type of thing........
I am injecting CO2 to keep up with water flow from tap which equilibrates makeup water to match tank pH. Water KH of tank and tap are nearly the same (measured). Tank and tap are ~20KH.
That's typical of a limestone well water, KH of 20 is very hard.
Often, such well water has high CO2 content, but it can vary as well.
I'll tell you my hypothosis...rapid significant blood pH swings DO cause physiological stress (supported by literature). Some organisms/species have developed better compensation mechanisms to hold blood/intracellular fluid pH steady in the face of environmental pH changes.
Test time:
pH change due to CO2 or due to Bicarbonate changes?
They are not the same thing nor have the same physiological stress.
Tell you what, take a fish, place them in a solution that has a pH change of 1 full unit via CO2 addition and then try this same full pH change using baking soda.
If you try and change the pH one full unit via baking soda, no one will argue that you will stress/kill the fish.
CO2?
Nope.
Heck, do not take my word for it, try it and see.
I can't answer why you or others' fish are or aren't showing symptoms...maybe my fish are just watching more violence on TV (guess I'll need to skip the news in the evenings!)
Controls, measures?
Well, we know that's not why.
How are you measuring the CO2?
pH?
What types of flow rates and surface movement do you have?
Measured the DO?
Use a chloramine based dechlorinator?
Some of these might be easy to address.
Some, not so much.
I typically suggest enough surface movement not to cause the water to break. This causes some CO2 loss, but that's easy to add more. However, it does make sure there's enough O2 coming in from above/the air to ensure that there's plenty for the fish, hopefully 5.5 or higher at all times, ideally 7-10ppm in a planted tank(7 early, 10 right at night fall).
Stable good CO2, can easily be at 30ppm, provided the method to measure it is accurate.
CO2, O2 and fish respiration involves not just CO2, it involves all three things.
Circulation is yet another one.
I think adding better circulation would help, are these fish acclimated well to a KH of 20? Temps the same? Do smaller % water changes cause issues?
Is there copper in the tap water?
There's all sorts of things to look at here.
I think it's wise to rule things out one by one, while you might not get at what's causing the issue, you will have at least narrowed it down considerably.
Then you have few suspects and can approach the issue from there.
References and science:
Take a look at Poxoton and Allouse 1982 for more on CO2, pH and toxicity.
Alterations in the blood pH of fishes can be corrected by the exchange of ions between their internal (blood) and external (water) environments. The most important site of ion transfer are the gills.
Okay, not too bad so far:
This ion exchange involves external Cl- for internal HCO3-, and external Na+ for internal H+.
Blood acidosis (low pH) is corrected by reducing the uptake of Cl- by the gills and to some extent increasing uptake of Na+. The reduction in Cl- uptake thus reduces HCO3- excretion, and the increase in Na+ uptake increases the excretion of H+. The net effect is a compensatory increase an return to normal blood pH.
However, the ionic content of water can affect ionic transfers across the gills. Of most importance is the availability of the appropriate counter-ions for exchange: Cl- and Na+.
Also, high water H+ content (low pH) limits the ability of the organism to excrete H+ and thus maintain adequate internal pH levels.
This is what you are suggesting is occurring?
But we typically have higher pH and KH's, the CO2 is added artificially with a high KH.
Discharge of acidic compounds(say CO2) into water with high carbonate alkalinity will cause the production(or simple addition in our case here) of high levels of dissolved CO2 without significant changes in pH. These high levels of CO2 can have direct toxic effects in fishes(toxicity is about 100ppm for most fishes at pH's between 6.5 and 8). For example, a correlation between high water levels of CO2 and nephrocalcinosis (calcium-based kidney stones) has been shown in trout farms.
Now since you have high KH, and a small change in pH= large changes in CO2.
Careful measurement might be an issue, tap water might have many things other than KH, might not be much Na or Cl, although I do not think so.
Now pH change:
Aquatic animals have very low blood levels of CO2
(bicarbonate) compared to terrestrial animals. The key reason is that fish
must circulate large volumes of water over their gills to get O2, and water
dissolves CO2 about 200 times more rapidly than O2. Thus, CO2 diffuses
rapidly into the water via the gills so that there is only a small difference
between the levels of CO2 in arterial blood and the surrounding water (Hoar, 1983).
Thus Fish can rapidly adjust to pH changes due to CO2 concentration differences. They cannot do this nearly as fast with bicarbonate.
You can test this experimentally and prove it to yourself.
O2 and CO2 respiration is a big issue as well, but different than the pH issue.
again, CO2 is extremely soluble, O2 is not. So fish pass a lot of water over the gills to make up for this.
You need to be willing to test, measure and provide controls, measure the tap water's parameters as well as sacrifice some fish, shrimp etc to see.
Few aquarists are willing to do that.
I prefer to use Shrimps as they are easier and generally more sensitive.
Still, how is it that the rest of the hobbyists do large water changes in CO2 enriched systems and never have an issue for decades?
You are not going to argue that we are all wrong and have been for decades while your one tank is the root cause for the fish deaths you have.
I'd bark up another tree for a reason/cause.
Regards,
Tom Barr
