· Premium Member
That is both the big advantage and the big disadvantage. Every time you add water you have to reconstitute it back to match that in the tank. If you don't do this you subject the fish to wildly varying hardness and total dissolved solids, which is not good for the fish. You also need a container to hold change water while you do the reconstituting before adding it to the tank.Agree RO/DI is a pain in the neck, the big advantage is you control Exactly what is in your water.
It is very beneficial to both the plants and the fish to do regular big water changes, so anything that makes it harder to do that will soon be a royal pain in the neck, and will probably discourage you from doing the water changes often enough.
RO/DI water, in my opinion, is for those with tap water that just isn't usable for plants and fish as it is. Then there is no other choice.