Do you only continually top off with RO water to keep the params the same or is the RO mixed with a small amount of remineralizer to add some minerals back? Even with pure RO top offs, won't you get a TDS creep eventually?
In Japan, we simply just top off with tap water since the water is idealized for shrimp keeping.The key is just to keep the water parameter stable.
I top off my tank with pure RO but in a small amount every 2days so it won't disturb the shrimps. In addition, I use water conditioner to stabilize my parameter (black control).
I think everyone probably have their own method. I'd recommend test then adjust since the water source, substrate and filter system are different.
What is TDS? What is PPM?
Where do I get RO?
TDS : total dissolved solids.
ppm : parts per million.
RO: reverse omosis.
I'm sure there are lot of topics about this if you do a little search in the forum.