Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish (probably shrimp, too, but I am not sure) are not so picky about pH.
What makes the difference is the mineral and salt content of the water.
Fish regulate the amount of water, minerals and salts in their cells, and adapt to the level of these materials in the water. This is the Total Dissolved Solids.
If the TDS of the water changes, fish need to change the way they deal with the water/mineral/salt balance in their cells. Small changes are easy to adapt to, but larger changes take time. When the change is sudden (like a water change with the wrong water, or moving them to the wrong tank) the fish cannot adapt so fast, and they die.
If you have a tank and fish with a certain GH, KH and pH, and you do a water change that results in the TDS, GH or KH rising, you can make a change that is up to 15% higher, and the fish can adapt OK. It does not matter what the pH is doing, as long as it is anywhere within an acceptable range.
If your tank has harder water than the new water you can make a water change that results in 10% lower TDS, GH or KH and the fish will handle that just fine. Again, it does not matter what the pH is doing, so long as it is not widely out of the range the fish can handle.
For fish, the pH can rise suddenly or crash from CO2, and this is fine with the fish. If you alter the pH with salts, acids, buffers or similar materials you are adding to the TDS of the water, and the fish may not be able to handle that. It is not the pH, or the sudden change in pH, it is the changing levels of TDS.
Set up a tank with ADA or similar product.
This substrate (and a few others) will remove the carbonates from the water.
Lower KH means the pH is more free to change. Other things in the water will alter the pH. 'other things' might be peat moss, Indian Almond Leaves, CO2, certain buffers like phosphate and products like pH Up and pH Down, and so on.
The tank adjusts, the fish adjust (the substrate removes the carbonates slow enough for the fish to adapt).
Then you want to do a water change, and the water has higher KH than the tank. Higher pH, too.
1) Test the TDS of tap and tank.
2) Test the GH of tap and tank. Sometimes the plants are removing enough calcium and magnesium to make some changes in the GH.
3) Add whatever you want to the new water to make the GH the same as in the tank, and add aquarium fertilizer.
4) Test the TDS again. If it is as much as 15% higher than the tank that is just fine. You could do a 100% water change, and the fish will be fine.
If the TDS is more than 15% higher, you will have to do the math to see how big a water change you could do.