I agree that
DI is the way to go. If you want to use it for aquarium use only, you don't need the small pressure tank. If you want to use it for aquarium and drinking water, you'll need the pressure tank and a larger storage container with a float valve...if you want it to be convenient. You can run the
RO to the drinking water tank and the
DI to the aquarium storage container. I would look at the Aqua FX Barracuda for several reasons. Yes, it is more expensive, but not that much. You'll get an aluminum filter bracket...most everyone else uses steel. Aluminum will hold up to corrosion much better. You get a built in pressure gauge...this tells you when the prefilters are clogging up and what your home water pressure is. You get all clear filter housings so you can see all the filters and judge their condition. You get a color changing
DI cartridge in a clear housing...it changes color as it is used up. You get an inline
TDS meter so you can, at a glance, monitor your units performance. You can add the drinking water kit and/or a food grade storage container with a float valve preinstalled. Although it does come in a 50gpd rating, for about $20 more, you can get it in a 100gpd rating. Anyway, although it is a more expensive unit, I think it's well worth it. The most important thing you get with one of these units is customer support from people who know what they're talking about and are willing to do whatever it takes to help you. I've never called them and not gotten an answer. I've never asked a question of them and not had it answered...that's worth a good bit to me.
JMHO.