RO/DI and other random questions

[mike31154]

Originally Posted by Sea Witch

I have a few questions so I thought I'd lump them all together.

For buying an RO/DI unit,

1. What should I be looking for?
2. Is there a big difference between brands?
3. How much should I be spending for a 100gpd unit?

and unrelated,

4. What kind of filter do you folks use on an H or Q tank?

Thanks

From what I've seen on the board here, you folks on the coast & island have very low TDS source water to start with. You may be able to get by at a reasonable cost with DI filtration only. First thing to do is buy or borrow a TDS meter and check your tap water. If it's really low, say <20 look into DI only. Also a good idea to check your water pressure to determine if you might need a booster pump. If your pressure is at least 50-60 psi, you should be good without booster.

1. See through cartridge housings for pre filters & DI. RO membrane housings are all white, no choice there. Dual TDS meter included, pressure guage included, although you can get that locally after market fairly easily. Number of pre filter stages will vary depending on your requirements. Chloramine treated water will generally require an additional carbon stage, whereas with chlorine, one will suffice. DI cartridge should be mounted vertical as opposed to horizontal, more efficient that way.

2. Can be, but most systems are assembled by the vendor from generic components. The RO membrane is fairly important, seems the DOW Filmtec is one of the best, so look for that. Cheaper systems will tend to have white pre filter housings and poorer quality pre filters. They may also have lower quality carbon stages. These can easily be replaced later. Pre filter should be at least 5 micron.

3. In the $250 range for a quality system with most of the options I mentioned in 1. Pre filters, housings & membrane will all be top notch. Better to go for 75 gpd since the rejection rate is higher for that membrane than the 100. Might be a little slower in production, but TDS will be lower out of the membrane, before the DI stage.

4. Can't speak to this, I have neither, been rolling the dice with additions and so far OK. Fish that have died on me would not have fared better in a H or Q. One power head victim Lawnmower Blenny, one carpet surfer Lawnmower Blenny, two starved Lawnmower Blenny, Copperband Butterfly & some Damsels - Blue Devil & Chromis that just kept taking each other out. Needless to say, for the sake of Lawnmower Blennies I've given up on keeping one, same goes for Copperband, they're way too iffy and shouldn't even be offered in the trade IMO. Never had an issue with corals.