[mike31154]

I personally don't have the type of storage tank you're referring to if it's one that comes with the system. But if so, I think they're generally meant as a drinking water add-on to the system. They have an internal bladder that keeps the tank pressurized so you can draw drinking water from a small tap which is also added on. Not sure it will hold sufficient volume for your aquarium water change needs. I think these tanks are also normally plumbed in after the RO membrane, not after the final DI stage, since that's real bland water and most people advise against using that for drinking purposes.

I guess cost of the tank is the only con really. I just have a tee with valve in the line between the RO output & DI input. Whenever I want pure water for the coffee machine or whatever, I divert from there, before the DI, and fill it into a plastic bottle.