RO/DI vs Just RO??

[awillemd1]

Can someone help me here? I have an RO system in my house that I have been using to replace evaporated water and for water changes. If I test the water with my Salifert PO4 testkit, it shows 0 phosphate. Would I still benefit from putting a DI unit on the end? :? What is the role of the DI filter after an RO unit? Is it to remove that last little bit of phosphate that the RO doesn't remove which could build up over time?

Thanks in advance.

awillemd1

 

[RogerMcAllen]

RO is basically a really fine filter that strains out just about everything. Some ions can get through, so the DI takes these ions out leaving you with absolutely pure water.

 

[awillemd1]

Thank you for your reply!

I guess my confusion comes from a recent post on this site and a conversation I had with a coral supplier. They both seem to indicate that in order to be sure you don't have any algae problems you need an RO/DI system. So do you need to have the DI system to be sure you won't have any algae problems, i.e. to remove the last little bit of phosphate? :?

Thanks in advance.

awillemd1

 

[fishfreek]

The difference is rather low if you ask me. What your talking about is the difference between lets say 98.5% pure water and 99.5% pure water.

 

[ReefLady]

I agree with Fishfreek. Also, my understanding is that the final *polishing* that is done by the DI cartridge is what typically removes the remaining phosphates and silicates. If you're already testing zero for these, then I'd forego the DI.

JMO

With our lovely rural well water, we use a double DI (2 DI cartridges), and it is only after the last DI cartridge that we reach 0.00 p04, and 0 TDS (from an initial pre-RO/DI reading of 275 TDS, and p04 off the charts.)