Wondering why RO/DI water is soo much better than just RO water.

[Dangger]

My understanding is the Sediment, Carbon, and RO filters greatly reduce the TDS in your home water.

I understand DI will bring is down to or close to Zero TDS. Is this really necessary or is it just a numbers game and we as reefers try to perfect everything?

Is it true the RO/DI water sitting in a container will have its TDS raise over time since it's pulling ions out from the container itself and try to reach equilibrium? Doesn't this tell us that RO/DI water is a bit excessive?

 

[Reefried]

While true that the tds can raise in your storage container its still much better to use 000 tds water than tap or other.....but the main thing a rodi is doing is removing phosphates and silica which are both detrimental to a reef.......and say what u want about 000 tds but my di resin recently went and the water was at 002-005 I said what the hell and used it for top off for 2 months and I saw a little cyano outbreak and I exhausted my carbon and gfo quicker too so replaced the di and I'm back to 000 and that's what ill use forever now.......granted that 002-005 isn't that bad and corals were still happy but my system was use to 000 so I saw the effect of using the higher tds water.

 

[Reefried]

And I'm not sure as my top off container is only 2.5 galls so I use it before it rises too much but if u keep the rodi water moving it pulls less tds from the container. (I think)

 

[The Ng Thing]

I find the more things I do to my tank the worse it gets in terms of carbon and special water. (Just as an observation and not a recommendation) I don't use carbon and I use tap water for my water changes and top-off. FWIW our house does have a sediment/carbon filter on the mainline. I've only had a hair algae outbreak once and after a couple of turbos & some new feeding methods the problem was eliminated. I'm sure 0 TDS is helpful but not entirely necessary in some circumstances. There are so many factors that make it hard to say that A is a definite cure for B. I agree 0 TDS is better than any TDS but I think you can get away with a low reading and still have a healthy tank. In my opinion I do think it is a little excessive.

 

[Reefried]

well my tap water is 076-085 tds so i would NEVER put that into my reef.

 

[Jocko]

well my tap water is 076-085 tds so i would NEVER put that into my reef.

Are you referring to your 10 gallon nano tank?

I mean you raise a good point in that people should feel free to try different things and see what works for them. There are an endless number of variables. Which is part of the problem with asking for advice. You sort of have to sift through it all and figure out which might apply to you and which to take with a grain of salt. For me personally, I started to get more and more hair algae. Finally it occurred to me that I had not replaced the filter cartridges in over a year. I swapped them out and within days the color of the hair algae started to go from bright green to brownish. And it stopped regrowing in the areas I pulled it out.

In regards to the OP's question: I guess I don't see what the issue is. To me if any part of the RODI process is a problem, it's the RO part. That's where the massive water waste is happening. That's where the more expensive membrane is that you have to take care of. Focusing on the DI cartridge, I guess I don't see the big difference between buying 4 replacement cartridges (1 sediment, 2 carbon, 1 DI) vs. saving a few bucks and only buying 3 without a DI one.

 

[JohnK]

IMO there are a lot of takes on this subject, as well as a lot of variables that affect it.

For one, TDS is a very non-specific measure. TDS tells us the total amount of dissolved solids, but tells us nothing about what they are. One person may have 100 TDS but none of it anything all that harmful. Another might have a lower number but much of it might be toxic metals or other really nasty stuff. A lot depends on the local water supply.

Whatever the case, I think it is also important to keep in mind that we are using this water as top off, and that means that whatever the TDS in the water we add to our tanks is made up of, those solids will become more and more concentrated as water evaporates out but the solids don't.

As far as the question about how important the DI is when most of the TDS is removed by the RO unit, it may depend a lot on what is actually getting past the RO. IIRC I have seen some discussion coming from more chemistry minded people than myself that at least alluded to the idea that certain things are more likely to get past the RO than others. Maybe a good question for Randy at the upcoming meeting?

Personally, my tap water is near 400 ppm so I'm definately not putting that into my tank.