Which is more important? RO or DI?

[MizTanks]

Correct me if I'm wrong. First the water goes through the DI resin and then it is pressured through the RO filter?

I know the DI filters out the bigger contaminants and what that doesn't get the RO does?

So can I use a DI filter only or just an RO filter?

[Paulo]

Ro first then it goes thru DI. DI wont do anything for chlorines and smaller stuff. RO IMO is the most important. People have tanks that they have not used either with success. Just depends on their water source.

[CalmSeasQuest]

By far, the best answer is both, but if you HAD to chose - An RO would be the best/only decision. A quality, properly configured RO can remove up ~98% of the TDS in most water with the DI resin removing the remainder. It would not be feasible to use just DI in most scenarios as it would not provide the mechanical and prefiltration of the RO and would exhaust itself almost instantly becoming cost-prohibitive.

We work so hard to limit/remove nutrients and contaminants from our tanks, I shudder at the thought of knowingly introducing them with every gallon of fresh salt or top-off water.

[MizTanks]

Would this unit do?

Reverse Osmosis Water Filter Systems 4 stage 36 GPD | eBay

 

Reverse Osmosis Water Filter Systems 4 stage 36 GPD | eBay

[Heidi]

yes that would do but for like $10 more you can have this...
Aquarium Water | Reverse Osmosis | RODI Water | ReefKeeper Water | Mighty Mite 50GPD with DI Added

RoDi combo for little tanks it has pretty awesome reviews you can get a coupon from them cause they are a sponsor.

$0.02

[zenpytho]

pure water club 6 stage rodi $109 100 gpd its what i have works great havent had any trouble

[rmalone]

Theoretically you could run only DI and get water spotless....But it would cost an arm and a leg, because you would exhaust the resin so fast. Overall if I had a fish only tank I would only use ro, if I was on city water and had a reef tank, I would consider the same. On a well where the tds is likely 300ppm or more (which is most of south east michigan), ro +di is by far the best bet. Can a person get away with straight up well water? YES but it makes no sense to do so. Water is a small price to pay in the big picture of a reef tank. RODI for all reef tanks using well water just makes good sense both in dollars and reduced headaches. There are a million threads on guys using straight well water with nasty algae issues, yet they test 0 on nitrates and 0 on phosphates (which is another whole issue altogether).

[MizTanks]

Originally Posted by Heidi

yes that would do but for like $10 more you can have this...
Aquarium Water | Reverse Osmosis | RODI Water | ReefKeeper Water | Mighty Mite 50GPD with DI Added

RoDi combo for little tanks it has pretty awesome reviews you can get a coupon from them cause they are a sponsor.

$0.02

Very sweet unit Heidi~My penny bank is a 1/4 there

[AZDesertRat]

Neither RO or DI is particularly effective at removing certain contaminants so it really takes both to do a good job.
RO is only marginally effective at all forms of ammonia including nitrites and nitrates, on the flip side weakly ionized substances like phosphates and silicates are tough for most DI resins.

If you had to choose one it should be a good RO.

I would think twice about the small "portable" RO and RO/DI units, they have major drawbacks. For one they use smaller non standard replacement sediment or prefilters, carbons and DI cartridges. These replacements are harder to find, especially in the low micron ranges reefkeepers prefer for our systems. They also do not last as long due to being smaller and most of all cost more to replace. Try to find a 1 or 0.5 micron prefilter and carbon block for a portable or a 20 oz DI cartridge

Along with that they really are not much if any smaller. They normally use the same top bracket as the full size systems so the footprint is the same, just a few inches shorter so no advantage really. Add to that they do not come with the necessary inline pressure gauge or a TDS meter and most do not have thingsmost of us find useful like an adjustable or capillary tube flow restrictor or a DI bypass valve so you can use RO only water for things like drinking or pet water.

What initially looks like a good deal ends up costing more to operate and often needs upgrades to function as intended. Add up the cost of more frequent replacements a TDS meter and pressure gauge and the cost exceeds the cost of a better full size reef quality system within the first 12 to 18 months. Most of us plan to keep our RO/DI systems for years so the long trerm operating cost is a big issue.

[MizTanks]

I'll be using it for tank water only, at 5g's weekly or biweekly. Does this not make a difference? Oh and it'll be attached to the faucet tap. We have great water here so I'm sure the filters will last longer then usual.