Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Test the mineral and other levels in the tap water.
GH, KH, TDS.
Most livestock do not care what the pH is doing, as long as it is within their preferred range, but the levels of the things measured by those tests need to stay as stable as possible.
Adding CO2, for example, is not changing any of those mineral levels, except, maybe KH, just a bit through the interaction of CO2 and carbonates. So small hobby test kits are not likely to pick it up,
Fish are just fine with the CO2 induced pH changes.
Aquasoil removes the KH from the water, allowing the pH to drop.
When you do a water change with water that has more than just a trace of carbonates, that is creating quite a change in the KH level in the tank. This can cause some issues.
Here are some solutions:
a) Add something to the tank mid week (more or less) that will maintain the KH at whatever level is optimum for the livestock and plants. Potassium bicarbonate, baking soda or other materials. This way, when you do a water change yes, the KH will be changed, but it will not be so extreme.
b) Use new water that is close enough to the tank water for GH, KH and TDS that there will not be more than about 10%-15% rise in these values. Most fish can handle that just fine. (I do not know how much shrimp can handle). Depending on what is making the pH so high in your tap water, you might have to use reverse osmosis water then add back just the minerals you want. Then monitor the tank through the week and add minerals as needed. That substrate is high CEC, and will remove minerals from the water, as you are noting with the carbonates.
c) Do more frequent water changes that will keep adding KH from the tap to the tank on a more steady basis.
d) Top off with tap water. This will also be adding other minerals, but the plants might be using them up, or they might not.