RO/DI units - which one?

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Aquarium Advice Freak
Jun 15, 2008
I have a 34gallon Solana aquarium. I want to get a RO/DI unit. Can you suggest a type / manufacturer? My water changes are every 2 weeks and it's 5gallons - so I don't think I need a very fast one.

I'm looking on ebay - but wow, there are so many types! 4 canister, 2 canister, storage tank, guage etc...
Since you only change roughly 100 gallons per year I'd personally recommend just using filtered water from a grocery store if it's available. Generally you can get refill water for about $.30-$.40 per gallon and keep it in the gallon jug containers. that would only be less that $30 per year for you seeing as how you'd want to mix the filtered water with tap water to get buffering capacity and some mineral hardness to the water. I'm not sure it's even necessary for you to have to buy filtered water let alone spend $75+ on an RO/DI unit. What are you keeping that you think you need special water?

FWIW the Brita filters and similar ones are capable of filtering 40-50 gallons of tap water and would still be less expensive for you than getting an RO unit if you wanted something available at home instead of having to refill at the store when you buy groceries. Generally RO/DI units are for people that change LOTS of water and people that are breeding. I change out about as much water in 2 weeks as you do in a year and I don't have an RO/DI setup. I keep discus/angelfish/red cherry shrimp in my water with a pH of 8.0, KH of 300 ppm, and GH of 300 ppm with no problems. My RCS colony is THRIVING and my angels look like they are going to breed in it too!
wow... well i do have a brita filter... i just always read and hear horror stories of how you HAVE TO have ro/di or you will kill everything. I only have a cleaner crew and just put a green neon zoo and finger leather zoo in the aquarium... it's 95% going to be a reef tank. right now i've been purchasing rodi from LFS at .50 gallon... so sounds like I should just keep doing that!
I didn't notice that you posted in the reef forum, my apologies. Lots of what I said pertained to FW but for SW I'm pretty sure that corals will need some "hardness" to the water. You won't want any chlorines/chloramines that's for sure. I'll let someone with far more experience in SW and corals chime in to help you. But if that's all it costs I'd continue to buy it from the LFS or grocery store if it's cheaper there (most likely is).
They make them as as low as 35 gallons per day. I would suggest getting one. Between top offs and PWC`s you`ll use more than you think. JMO
I like the Reefkeepers at

I don't own one, but it's on my wishlist.

There's the compromise solution of buying your own TDI meter, and testing the water you buy for quality. You can always talk to the manager of the store about maintaining the filter if it drifts out of spec.

You are not likely to kill anything using tap water instead of RO/DI, but you will be much more likely to be fighting algae, and RO/DI will filter out most contaminants that may creep into the tap. I have heard stories of people doing fine on tap water for a long time, and then having sudden major problems when the city/county changed something in the water.
Er... TDS (Total Disolved Solids) meter. TDI is the test my dog is studying for. (Therapy Dog International)
Just as a reference, for those in the FW trade. You have to buy additives to add back into RO/DI water for FW. The process strips everything out. RO-RITE is one product. Dumping 0 TDS water into a freshwater tank will result in very unhappy fish and quite possibly a few deaths (personal experience).

Also it's best to heavily aerate the water as well.

I went back to using bottled for my FW and RO/DI for my SW running GFO to get the Phosphate and Silica under control in the FW
I have really nasty tap where I live. For awhile I was using bottled RO to dilute the tap, and it was a good compromise solution. Can't keep that up now with the larger tank, so I keep looking at getting my own unit.
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