That's kind of what I do for my shrimp tank. I RO filter to get the mineral content close to zero, then add a specific amount of minerals to get the TDS to wha

That's kind of what I do for my shrimp tank. I RO filter to get the mineral content close to zero, then add a specific amount of minerals to get the TDS to what it would be in their natural habitat. There are RO systems which have a final stage to add minerals back into the water, but I don't know how well they actually work.