RO vs RODI water

[ha-y-n salt]

whats the difference between just RO water, and water that is RODI?

 

[bertoni]

RODI water goes through an extra filtration phase, deionization, that removes most charged contaminants. Depending on the input water, DI might be useful or not. I don't care to take the risk, and always use RO-DI.

 

[ha-y-n salt]

is it possible to add a DI unit on to an existing RO unit?

 

[bertoni]

Definitely. There are add-on units available from a number of vendors.

 

[IslandCrow]

RO, or reverse osmosis water has simply gone through a reverse osmosis membrane, making it pretty pure. . .I believe it removes somewhere between 95-97% of the contaminates. DI, or deionization is done by passing the water through a special resin. I don't know all the chemistry behind it, but it gives you very pure water, removing around 99% of the contaminates. The reason we do the RO process first is to lighten the load on that (rather expensive) DI resin so it will last longer. . .hence RO/DI water.
So, the abridged version is that RODI water is significantly more pure than just RO. Plain Deionized water would actually be the same purity, but ultimately more costly to do. Is RODI water necessary. . .that's a matter of some debate, but it can't hurt.

 

[ha-y-n salt]

thanks for the help.

 

[AZDesertRat]

If you already have an RO this is all you need to add DI:

http://www.purelyh2o.com/cart.php?target=product&product_id=17&category_id=13

 

[ha-y-n salt]

thanks again

 

[johnxboi]

just the topic i was looking for. so can you just use plain RO water? and waht is the difference between "aquarium" RO systems vs "home" RO systems.

 

[AZDesertRat]

In order to answer your question you need to know the quality of your raw water. Without that its hard to answer except RO/DI is always going to be the preferred water to use for a reef system. RO only waorks in some instances but you are usually best to do the final polishing DI gives it.
As for home vs aquarium systems, if you are looking at most inexpensive e-bay systems there usually is no difference. The vendor gets these units assembled from China and passes them off as a one size fits all. Now if you are looking at a vendor that specializes in reef systems they normally come with a better RO membrane, 98% vs 90%, better carbon filtration, 2 graduated micron sized carbon blocks vs granular carbon or non sized or non rated carbon blocks, and the good systems use a true 10" canister style refillable DI filter. Among other things they may also come with an autoshutoff valve, TDS meter, pressure gauge and float valve.

Cheap is not good when it comes to RO and RO/DI and you really do get what you pay for. There are lots of very good vendors out there and some do sell on e-bay, but don't expect to get a well made system for $69, it just doesn't happen.

 

[IslandCrow]

A couple extras I looked for when I bought my RO/DI system was a pressure guage and a flush valve. The latter can be bought separately and installed quite easily if you find a system you like that doesn't have one. A TDS meter is also a very good idea. I have one that connects into the input and output lines, so when I start my unit up, I can just turn the meter on and make sure it reads zero for the water coming out. If not, it's time to change the cartridges.
Also, in looking around, it didn't seem like the RO/DI systems were that much more expensive than just plain RO. I guess there's the long term expense of replacing the DI resin, but it seems well worth the extra cost. And in my opinion, the convenience of having an endless supply of pure water readily available more than makes up for the initial investment.

 

[CSRMUSIC]

I talked to the man who helped set up my water in my new house. He recommended just using an RO unit, saying the extra DI component is wasteful of water, and sometimes uses a harmful chemical to treat the ions. He said the small percentage that RO misses in treating the water is insignificant. Any insight on his comments? How does the DI component work, and is it wasteful or dangerous in any way?

 

[shifty51008]

when you recharge DI resion you use muratic acid and lye. these items can be dangerous to use if not careful which is why lots of people just buy new when their old ones run out.

for instance my tap water reads in the 400ppm range, after the RO filter i get a reading of 5ppm and after the DI I get 0ppm. some will argue 5ppm is fine to use and it may well be, but you don't know excatly what makes up that 5ppm, copper, nitrates, phosphates, ect. so IMO why take the chance with the 5ppm feeding the algae or adding small ammounts of harmful metals to your tank when it don't cost much to go from 5ppm to 0ppm.

as for it being wasteful, I don't understand how it is as you don't get any waste water from the DI stage

 

[Buckeye Hydro]

I talked to the man who helped set up my water in my new house. He recommended just using an RO unit, saying the extra DI component is wasteful of water, and sometimes uses a harmful chemical to treat the ions. He said the small percentage that RO misses in treating the water is insignificant. Any insight on his comments? How does the DI component work, and is it wasteful or dangerous in any way?

This advice doesn't make sense to me. DI doesn't waste water, other than the water used in manufacturing the resin.

Most plumbers have never heard of "DI", and only some of them have crossed paths with "RO"

Russ

 

[dkeller_nc]

I talked to the man who helped set up my water in my new house. He recommended just using an RO unit, saying the extra DI component is wasteful of water, and sometimes uses a harmful chemical to treat the ions. He said the small percentage that RO misses in treating the water is insignificant. Any insight on his comments? How does the DI component work, and is it wasteful or dangerous in any way?

I'll second Russ's comment; the person that you talked to has, in fact, got this exactly backwards. Reverse Osmosis is a form of tangential flow filtration, where the upstream side is pumped past a membrane at high pressure and then exits the system through a flow restrictor. Water permeates through the membrane to the product side, but dissolved ions and bigger organic molecules can't diffuse through the membrane's pores, with the net effect of "rejecting" most dissolved substances.

If the system was set up as a "dead-end" filter such that all of the water that goes in the upstream side was forced through, the membrane would clog with precipitated calcium and other ions very rapidly (as in minutes). That's why RO is "wasteful" of water - the majority of the water goes out of the flow restrictor to sweep out contaminants and to avoid "fouling" the membrane. Most home systems are set up with a 4:1 to 6:1 waste to product ratio.

This reject water, though, is perfectly suitable for watering plants, washing clothes, filling bathtubs or just about any other use you can think of, if you choose to do so.

Deionization resin filtration is 100% efficient - all of the water that goes in comes out as highly purified product water. The "resin" that we use is actually a combination (50:50) mixture of a strong cation and strong anion resin. The cation exchange resin has negatively charged groups on its surface, and removes positively charged ions like sodium, calcium, magnesium, copper, etc... The anion exchange resin has positively charged groups on its surface, and removes negatively charged ions like phosphate, sulfates, nitrates, etc...

Reverse osmosis membranes aren't used with deionization resins just to remove most of the ions and thus make the resin last longer; RO will remove many organic contaminants, and unless the deionization resin is modified in a particular way (which is not common), it will only remove charged contaminants.