[fishnut]

Fish and plants cannot live in pure RO water.

There are 2 ways to make RO water suitable for FW fish and plants:

one way is to use 80% RO water plus 20% tap water

the other way is to use a product to re-constitute the RO water (add back minerals) such as Mark Weiss Recon 50 or Kent R/O Right

Also, it is important to keep the dKH = 4 degrees at a minimum, in order to keep the pH from falling suddenly to unsafe levels.

Pure RO water has no buffering capacity by itself.