I just bought the new RO/DI unit Dakar is referring to. I saw it on ebay, but dealt with the company directly after doing my research on various units...this IS the best one by far-plus the filter canisters are clear so you can better monitor their wear and tear. You can call the company directly at 714-953-9009 and pick their brain. Ask for a technician...they knew the most. Also, make sure you tell them the water is specifically for your tank; that way they thow in the second DI filter. If the RO/DI unit is used for drinking water, this final 6th stage is different to re-intoroduce some minerals for flavor. Mine was $150, including shipping. I also got an automatic shut-off float for my 10gal container, a hose-adaptor, and a preasure-regulator (anything over 80 could pop the unit, and reduce your water quality). All three extras were a $20 total. They have replacement filters too if you want to price that route.