RO water, confused !

The most popular RO membrane by far is the 75 GPD Dow Filmtec, it is the same physical size as a 25 or 50 GPD, makes the same 96-98% pure water much faster so less waiting around and usually costs the same or within $5 of the slower ones.

You will want a normal full sized RO/DI system. While the compact type systems look attractive to fisrt time buyers, those on a budget or who live in an apartment or rented home, they really are not a bargain at all.

Most of the compact systems use the same top bracket as the full size systems so the footprint is the same, just a little shorter since the filters are mounted horizontally on top instead of vertically on the bottom, maybe a 4-5" vertical savings. The biggest disadvantages are the throwaway type filters they use do not come in many of the more desirable micron ranges reefers prefer so do not filter as well, are smaller so do not last as long, are not as readily available and generally cost more than standard 10" size replacement cartridges that fit in standard clear canisters. Usually they do not come with the troubleshooting and operatioal tools you will need like a TDS meter and pressure gauge either and some are lower GPD so take longer to make water.

When you look at it like that what it comes down to is shorter filter life so higher long term cost of ownership.

You want a standard 4 stage RO/DI with full size vertical 10" canisters, a 75 GPD RO membrane and a 10" vertical refillable DI. It should include a TDS meter, either inline or handheld (I have both), an inline pressure gauge and its preferrable to have an adjustable flow restrictor so you can fine tune the system for your exact water conditions.

Take a look at the CSP-DI found here on sale for $145:
SpectraPure Customer Appreciation SALE! 20% - 50% off

Or the 75 GPD Premium found here:
www.buckeyefieldsuply.com

Both fit exactly into what I said above.

Others to consider are the Optima Vision here:
www.purelyH2o.com

or the 100 GPD Reefkeeper found here:
www.melevsreef.com

The last two may require buying some extra pieces like a TDS meter and pressure gauge but they are good systems too.