Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Test tap and filtered water for GH and KH. Set a balance that suits the fish by combining RO (filtered) and tap water. Ignore pH.
If there is more ammonia in the final product than Prime or similar dechlor can handle, then you may not want to use the water that adds the ammonia. (tap water)
If the ammonia is just from chloramine, then Prime can deal with it. Probably do not need to fertilize with KNO3, if the tap water + RO blend gives you enough nitrogen.
One possible recipe:
1 part tap water + 3 parts RO.
Probably the test results will show:
1 ppm ammonia in the mix.
I would use a single dose of Prime (measuring the whole volume of the mix, not just the tap water portion) for that much ammonia.
Make sure you have the right test for ammonia. Some ammonia tests do not show you how much ammonia is locked up vs. how much is free.
Also, if you can get the pH into the acidic range, the ammonia is present as ammonium (NH4+) and is less toxic.
Mollies are hard water fish, thriving in high GH, high KH water, with an alkaline pH.
Most Tetras, and many Barbs are soft water fish, thriving in low GH, low KH water, often with peat moss filtration to replicate black water conditions. Not compatible with Mollies.
Most plants can handle a wide range of conditions as long as the minerals they need are present. Usually this is enough if the GH is over 3 German degrees of hardness.