Effects of ph shift on fish

Hi Prof

I'd like to ask your expert opinion on the above topic. I have now read some literature and the general conclusion I make is that changing the ph by adjusting the CO2 levels does not affect the fish health. Let me explain:

If you have 7ph and 4kh, you have, according to the famous table, 12ppm of disolved CO2 in the water. Now you inject CO2 to 30ppm and the ph drops to 6.6. But because the kh remains constant, the disolved salts do not change, and thus there is no impact or osmotic stress on the fish.

Another example: you start off with 4kh and 6.6ph in a CO2 injected tank. You are basically running 30ppm CO2. You have never done anything to alter kh, it is the same as your tap water. Now you do a large water change of say 50%. Your tap water is 8ph and non-CO2 enriched. The ph in the tank now shifts to around 7.2; the fish are still fine. Why? Because the kh did not change and thus there was no osmotic stress on the fish.

Do I understand the above correctly? If so, then it must be argued that changes in the ph resulting from changes in the CO2 is not detrimental to fish health, as long as the kh remains constant. This is exactly what happens in a CO2 injected tank. With a ph controller one can keep the ph constant and thus vary the CO2 content. With a timer one can switch the CO2 off at night and there will be shifts in the ph.

All other methods of altering the ph of a tank has some effect on the TDS, thus leading to osmotic stress and posing a risk to fish health.

My question is: based on what I described above, can you confirm if these shifts in ph (when you run CO2 on a timer) are actually dangerous to fish or not?

Regards
Lauré

 

Hi Lauré,

Thanks for an interesting and very appropriate question.

Your arguments with regard to the kH and the fact that it does not change during CO2 fertilization is perfectly correct and you are also correct that this as a result does not have an effect on the osmotic pressure of the water and therefore does not cause osmotic stress.

However, pH is a measure of the concentration of hydrogen ions, or H+ ions, and this does therefore have a very profound effect on the osmotic conditions and therefore the osmotic stress on fishes. To complicate matters, the pH scale is a log scale as you would know and at a pH of 6 in comparison to a pH of 7, the hydrogen ion concentration is 10 times as high. At a pH of 5 in comparison to pH 7 the hydrogen ion concentration is 100 times as high and so on. kH is measured on a linear scale so kH of 6 is one and a half times as large as a kH of 4 so the differences are not nearly as great and do not have as large an effect as pH does.

What I am saying to you is that the kidneys of a fish have to work much harder to equilibrate H+ ions as seen on a pH scale than kH values. Fluctuations during the day and night cause the fish's kidneys to have to work up and down and cause considerable osmotic stress. Additionally the blood of all living organisms including fishes is buffered at 7.2. This is absolutely rigid, change the pH by 0.1 of a pH unit and the red blood cells will pop. In the blood carbonate is used for buffering of the pH and the body makes this carbonate using an enzyme called carbonate anhydrase. H+ ions are taken up directly by the blood via the gills and changes in pH therefore have an immediate effect on the blood. If a fish is exposed to changing pH on a daily basis this enzyme system works incredibly hard at adapting all day long and this uses a tremendous amount of energy. What this means is that you are draining the energy reserves of your fishes.

If you read the aquatic literature you will see frequent mention of pH shock when moving fish from one aquarium to another and the one system differs from the other with regard to pH. It is warned that you should adapt pH slowly or else fishes will suffer from this shock. With pH differences of greater than 2 pH units you can expect this to cause problems particularly as catching the fishes causes considerable stress additionally. If you would be changing your pH to the extent that CO2 fertilization can and does, you would basically be exposing your fishes to pH shock on a daily basis.

In addition, I can mention that if one keeps discus in soft water, the pH tends to drop rapidly because heavy feeding will result in the release of high levels of ammonia (NH3) which in the biological filter will be converted to nitrate (NO3-). During this process, H+ is released leading to a pH drop. You can easily drop the pH to 4 within a week and then if you do a water change the pH goes up to pH 7 in other words a 1000 fold decrease in H+ ions. As this change would happen once a week the fishes can cope with this for a while, but then they start to decline and slowly but surely parasites and flagellates start attacking the fishes and getting the overhand. I have seen this over and over again and this pH and therefore osmotic stress plays a massive role. I actually believe that this is the primary reason for many of the problems folks have in keeping discus.

What I am saying is that pH changes caused by unregulated CO2 fertilization will shorten the life of your fishes. In my opinion, the only way CO2 fertilization can be applied is by means of pH regulation. This is expensive, but there are no short cuts. Equipment suppliers are perpetually trying to sell all sorts of short cuts without regulation, but all of this puts your fish at risk.

Kind regards,

Dirk

 

Hi Prof Dirk

It is good to see you active again; I was wondering why you were so quiet! Thank you for the informative response. I sent you a pm...