Before I got hooked into the planted tank, I would do weekly water changes of 20-25%, but no matter what I would do my p.H would never move. Always around 7.4-7.6. Now as I am messing around with getting my CO2 correct, the pH sometimes will be all over the board between 6.6-7.4. Yet, luckily I guess, my fish seem completely unaffected. Ironically, when i started adding some plants, before CO2 my pH seemed to go up to about 7.8, probably because they were extracting what little CO2 was in the water.

Should I be concerned about these fluctuations and their long term health on the fish? My fish all generally would prefer the slightly acid conditions (angels, tetras, bn plecos, cories). Or am I just paranoid?

Fred

It is an accepted fact that pH changes that occur due to dissolved CO2 in the water are not a problem for fish. I think the whole emphasis on obtaining the right pH for fish is way over blown. Too many people have had great success with "pH sensitive" fish when their pH is far from the recommended level. Like a lot of the old rules the pH rules were not correct.

We use CO2, which fish have in their blood and regulate rapidly, vs salts, like Alkalinity, HCO3, which they do regulate, but it does not appear and diiffuse out in a similar fashion.

Put another more practical way:

Take a large tank using CO2, the KH is say 5, the pH is say 6.6 and a GH of say 9.
Do a large water change, say 50-70%.
The incoming non CO2 enriched tap has a pH of 7.9.
KH for the tank and the tap is still KH= 5.

Result: fish are always fine.

Conclusion, pH shock is a myth.
It's not pH. It's the difference in salts in the KH mostly and the GH perhaps.

Next, try a KH of 1 and a GH of 1: results: generally not too bad. Fish can slowly acclimate from hard to soft.

Next, try from soft to hard, go from KH= 1 toa KH of 10.

Do this rapidly: dead fish.

pH can be kept the extact same level using CO2 or other acids or buffers for both treatments.

The ability of the fish to adapt to salts, rather than pH is the real issue here.

When fish only folks discuss pH, they usually mean KH differences, as they correlate with pH, more KH= more pH.

But when we add CO2, or look farther into the real issue, we find it's not pH by and of itself.

This can cause confusion and start heated debates as one person claims what they have been taught for 30 years must be right, while another that test and sets up practical test can clearly demonstrate it cannot be due to pH alone.

Some folks do not like me for this approach, nor questioning basic questions in the hobby, but I'd prefer to be right and have a better understanding than a big ego/and yell louder than the next person and take it personally as many often do.
Watch, see who actually answers the questions about the topic and who avoids them.

Do not be swayed by belief or weasel words.
Stick to what makes the most sense.
That's how you learn and that is always on topic.

Regards,
Tom Barr

Thank you, that may be the most thorough and understandable explanation I have ever heard of this topic. Since the CO2 does not affect the salts the change in pH does not result in any osmotic stress to the fish. Makes perfect sense. That also means that probably some of the pH down products are far more dangerous then the higher pH of the water.

I appreciate your approach, from what I can tell a lot of published information out there is based more on speculation and conjecture rather then science.

Fred

Well, I have far more to discuss about this topic and want to make sure everyone in the hobby has a good understanding about it.

I'll write more later on this.
But, the above is the simple practical test any hobbyists might do that is very specific for this situation.

Many lab studies are not this specific and do not test the species we keep.......

Regards,
Tom Barr