Question about RO water

You want RO/DI.
DI removes silicates another food for diatoms (brown algae).

 

If you're a starting SCUBA diver, buying your own gear is at least a couple of grand. Or you can rent everything you need to dive for about $30 per dive. If you only dive once a month, $30 a month isn't going to send you to the poor house. The other side of that argument is "Why not just spend the 2 grand and only pay $5 per dive to have your tank filled with air?"

You see?

If you'd rather pay $30 per month, and never have to drop the 2 grand, then just rent the equipment and don't buy.

In my opinion, though; why not just get it over with? If you're going to keep a reef tank, not only is the $200 or so you're going to spend for an RO/DI worth it, it also keeps you from being a slave to the supermarket RO/DI machines, or the LFS RO/DI water. Even when priced "right," you still have to lug several 40 pound-5 gallon containers home. Added to the hassle is getting the water into the tank. Oh, and not to sound distrustful of others, but when was the last time that supermarket changed those expensive filters in their RO/DI unit? And who's to say that LFS isn't selling you the water they're changing out of their disease ridden tanks? Sorry, but I have trust issues. I trust nobody but my wife, family, and Mission6.

With an RO/DI system hooked up right (like an auto top-off system), not only do you NOT have to lug water from store to home, but you never, ever, EVER again have to carry the weight of another gallon of water.

In conclusion, if you can afford it, get the RO/DI.

At the risk of sounding harsh; if you can't afford the $200 for a decent RO/DI, you're going to be cutting corners on a daily basis as a reef tank owner. This hobby is unforgiving enough with the best equipment. If you're straining to make ends meet buying what you need to sustain corals, then perhaps a reef tank isn't so wise. Stuff for reef tanks is expensive.

Good luck with your decision!