PO4 reading in RODI water?

StrangeDejavu · Oct 1, 2016

Not sure what to believe here. My filters were changed on my RODI on 7/26. My tap TDS is about 165. HM Digital handheld TDS meter and HM Digital in-line TDS meter both calibrated using HM Digital calibration solution. Both are showing 1 TDS in (after flushing for a bit) and 0 TDS out. I've been battling an unrelenting case of hair algae lately. I started running GFO, bought a Tunze 9001 skimmer and cut my feedings in half (to the point where fish started to lose weight), I feed LRS nano frenzy once per day and have only 2 fish in a BioCube 29. Nothing I do seems to make an impact on it except for the recent addition of GFO. That said, I was making water for a water change and decided to test this water for kicks. Hanna ULR is giving a reading of 0.14 but both TDS meters are saying this exact sample of water is 0 TDS. I rotate my filters out every 3 months but my membrane is over a year old. Is this a fluke or is PO4 really getting through?

cromag27 · Oct 1, 2016

What is your process of making water? start from the beginning. and what rodi do you have?

StrangeDejavu · Oct 1, 2016

cromag08 said:
What is your process of making water? start from the beginning. and what rodi do you have?

I have a SpectraPure unit. I disconnect the line before the DI and flush until the TDS reaches 2 or 1, then hook it back up and make water, usually a 5g bucket's worth. Add RC to 1.026 and let mix for 24 hours.

Some Google searching says to ignore the reading because apparently test kits aren't accurate at testing ultrapure water. I would imagine if that much PO4 is in the water (the sample was probably 30 mL of water) then I would get some kind of reading above 0.

cromag27 · Oct 1, 2016

How much water do you make at a time?

dgrigor02 · Oct 1, 2016

Can you clarify. Testing 0-1 tds ro/di water with ULR or mixing your salt then testing with ULR ?

cromag27 · Oct 1, 2016

Former. salt water will test way higher then 0-1 tds.

dgrigor02 said:
Can you clarify. Testing 0-1 tds ro/di water with ULR or mixing your salt then testing with ULR ?

dgrigor02 · Oct 1, 2016

Because ro/di has virtually no ions left it is very unstable. If your testing 0-1tds water with your ULR checker, I wouldn't trust the reading. Mix up your saltwater to 35ppt then test it for po4.

skim · Oct 1, 2016

Just so you know according to Hanna you CAN NOT use the ULR tester with Freshwater only Saltwater. Has something to do with the reagent.

StrangeDejavu · Oct 1, 2016

dgrigor02 said:
Mix up your saltwater to 35ppt then test it for po4.

Will do.

skim said:
Just so you know according to Hanna you CAN NOT use the ULR tester with Freshwater only Saltwater. Has something to do with the reagent.

Interesting, since it didn't say Hanna Saltwater like my Alkalinity checker, I figured it was good for both.

skim · Oct 2, 2016

So did a bunch of us and then one of the guys locally here contacted Hanna and that is what he was told.

cromag27 · Oct 2, 2016

The checker is absolutely for marine water.

But what concerns me more is using rodi water with any detectable tds.

mcarroll · Oct 2, 2016

Wasn't TDS 0-1 though? (I think counting accuracy and precision, isn't 0=1?)

cromag27 · Oct 2, 2016

"I disconnect the line before the DI and flush until the TDS reaches 2 or 1"

mcarroll said:
Wasn't TDS 0-1 though? (I think counting accuracy and precision, isn't 0=1?)

Richmond · Oct 2, 2016

Right, so his RO membrane take the water to 1-2 TDS and then his DI resin cleans it to 0-1... Sounds reasonable?

It's a horrible waste of DI resin to keep it connected while flushing the RO membranes.

cromag27 · Oct 2, 2016

But he never stated what his product water reads at. we can never assume.

And, that's not how to properly flush.

Richmond said:
Right, so his RO membrane take the water to 1-2 TDS and then his DI resin cleans it to 0-1... Sounds reasonable?

It's a horrible waste of DI resin to keep it connected while flushing the RO membranes.

mcarroll · Oct 2, 2016

cromag08 said:
And, that's not how to properly flush.

Can you clarify what you mean?

It does seem rough on the fittings and tube-end, so installing a valve would be a good idea....not sure if that's what you had in mind though?

blkhwkz · Oct 2, 2016

Proper way to flush? I take my DI resin out and run the unit until TDS comes down to 1-2 and then add DI resin back in. Some might say that is not the "proper" way, but it works.

mcarroll · Oct 2, 2016

And you are right there's no reason to assume anything during troubleshooting. We shall see how @StrangeDejavu responds.

But the OP is right that 1-2 TDS is about right for RO-only output – about 99.8% TDS rejection. The flush should be complete by the time TDS is down to that.

cromag27 · Oct 2, 2016

Sorry, got distracted.

To properly flush it needs to be done after you make your water. You want unrestricted water flow to run through the membrane to flush out any particles that may clog the membrane. run the water for 3 mins and you're done. you do NOT go by tds as the membrane tds will start to increase on its own naturally. Spectrapure makes a manual flush kit that's a cinch to install.

mcarroll said:
Can you clarify what you mean?

It does seem rough on the fittings and tube-end, so installing a valve would be a good idea....not sure if that's what you had in mind though?

cromag27 · Oct 2, 2016

Could be true, but to calculate the rejection rate we would need to know the tds IN figure as well (tap water).

And yeah, I'm kinda off the topic of po4 by now.

mcarroll said:
And you are right there's no reason to assume anything during troubleshooting. We shall see how @StrangeDejavu responds.

But the OP is right that 1-2 TDS is about right for RO-only output – about 99.8% TDS rejection. The flush should be complete by the time TDS is down to that.