Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If you will be moving the fish into the tank where you are using the RO water, then do not use too much at first. Make the parameters in the new set up just a little softer in the new set up. As you do water changes you can add greater % of RO until the parameters suit you (or your fish).
Beneficial bacteria live on all the surfaces in the tank- roughly 50% in the filter, and the remaining 50% on all the other surfaces- substrate, rocks, driftwood, plant leaves and stems, ceramic merpeople and so on.
The bacteria on the substrate are not down deep, but only in the top few layers of material. The area with lots of water flow for oxygen and ammonia to get to the bacteria.
The best way to save this is to skim it off first, before you get it mixed with the deeper substrate. You can add this to the new set up in several ways. If you like the look, just spread it over the surface of the new set up. If you do not want it in there, then put it in mesh bags and place them in areas with high water flow. Remove them one at a time each week for perhaps a month. This gives the bacteria a chance to grow in other areas without depleting the population too much.
You can also supplement the population by adding Nitrospira species of bacteria from a bottle.