Originally Posted by PaperclipGirl
I guess I was not so concerned about the frequency of water changes as so much as
"You pH will lower naturally if you don't change your water" advice....
** He did suggest that I buy a pH buffer, though so while not pushing frequent water changes buying water conditioner, he was suggesting I buy the buffer... not sure if that was more profit or not as I bought nothing.
Currently I am using driftwood, considering peat, and/or considering fish that thrive in pH 8 water
There is some truth in the statement that no water changes will lower your pH, but that is a very dangerous game to play and it risks the health and lives of the fish.
As the biological processes in the aquarium continue, they produce CO2 as do the fish. As the CO2 (carbon dioxide) increases, the pH will begin to lower. Organics will also build up with no water changes, which contributes further to this. At this point, enter the buffering of the water chemistry.
We talk of water hardness, which is the degree of dissolved mineral (calcium and magnesium chiefly) present in the water; tap water sometimes contains high amounts and sometimes not; you can also add calcareous materials (limestone and lava rocks, dolomite, crushed coral) to add calcium and this increases the hardness of the water in the tank. General hardness or GH is the calcium and magnesium measurement, in simple terms; KH is the carbonate hardness value, the amount of carbonates in the water.
If the water has a high degree of carbonate hardness--measured as degrees KH or ppm (parts per million) KH--it acts as a buffer to keep the pH stable. I am not a chemist, and I do not know at what point the buffering capacity of water will be reached, but it does occur. When that happens, the pH which has up to now been buffered and thus stable, can take quite a drop. This is very stressful to many fish, some will be killed outright, others weakened internally.
If the KH is low or non-existent, there is nothing to stop the pH lowering and it will continue to do so. Sometimes we may want this, and sometimes not. In my aquaria for instance, I have mostly wild-caught fish from the Amazon basin and SE Asia. These fish come from waters with very little hardness if any (some measure zero) and quite acidic, as low as 3.5 in some Amazonian streams. My tap water is pH 7 but zero hardness (GH and KH) so in the aquarium, due to the biological processes and fish I mentioned at the start, it drops steadily. In my 70g and 90g I leave it alone and it is at 5. In the 115g I deliberately buffer it with some dolomite in the filter and it remains at 6 (and GH at 2 dGH).
The effect of the regular weekly partial water change is to prevent the pH from falling too low. Not all fish can live in pH of 4 or 5, so this depends upon what fish you have. And if your tap water has some hardness [most does, but not all as in my case] a regular pwc will prevent the pH from dropping too much because it also buffers it. The pwc also reduces nitrates which can build up to toxic levels; though if you have plants this is not likely an issue as the plants use the ammonia/ammonium and nitrates are few or zero.
On the pH buffer, no. This is a chemical that does not belong in an aquarium with live fish. These chemicals may or may not work, depending again upon the hardness of the tap water and the tank water. A much safer method of controlling this is a regular weekly pwc of 50%. If you have live plants, this can be less and many planted tank aquarists do not do water changes this regularly. That's another matter.
If your water is pH 8, it is likely quite hard (though not always). This means the pH is not likely to lower by not changing water, but it will simply becomes worse and worse each day, literally poisioning the fish. Or I should more correctly say, possibly, because here again there is a lot at play. No two tanks are the same biologically. But the point that most of us would agree on, is that not doing a weekly pwc whatever the amount is long-term not going to benefit the fish and is bound to be detrimental in time, even if they may be hardy fish that can "exist" through it for a while.