Phosphate after RO/DI

I have been battling GHA for a long time. I have done all the usual stuff, GFO, 0 TDS, water changes (while pulling out as much as I can) beefing up the clean up crew, yada yada yada. So I am scanning the usual interweb fishy sites last night and run across a forum that has a dude with a similar battle as me...long story short, one of the contributors states RO/DI doesn't always remove high phosphates. So...I test my phosphates (with a Hanna checker) after my RO/DI unit and guess what? .02, what's up with that? What do you do if the RO/DI unit doesn't remove all the phosphate? Any insight any advice?:-[ How come I have never heard of this until now. I thought RO/DI took out all the bad stuff?

 

TDS tells you all you need to know about the quality of your RODI. If it's zero, so are the phosphates.

You can't test/measure RODI with our hobbyist test kits; you'll get false readings every time. There are no ions in it to allow a test kit to properly work.

 

So my water before the RO unit is .17 on the Hanna checker. After is .02 My TDS is zero for sure. I don't really have to worry about my source water having phosphates? That dude on the other forum was full of you know what, right?

 

The hanna checker is useless for measuring pure water. So, yes, that dude on the other forum was full of it.

I don't trust it for testing non saltwater. Same as you can't use TDS on salt water.

 

Alright, that all makes sense. I had a hard time believing I had made it this far in the hobby and never heard that. Unfortunately it would have explained a lot of the problems I have been experiencing.

 

So assuming my live rock is already laden with phosphates, how would I check this out? Take a piece of rock from my display and put it in freshwater or saltwater and then check with the Hanna after a couple of days?

 

bump

 

I don't think you really can check it... That may work, but I doubt it. too many factors IMO.

 

ok...this is probably very naive but could the RO/DI unit perhaps need to updated with new membrane or such? I know you said that TDS is 0 but you're reading phosphates on the RO? Just a thought.....

 

The RO unit seems to be fine, the guys earlier were saying you can't measure pure water with a phosphate meter because you will get incorrect readings, as long as you are getting 0 TDS there should be no phosphates present.