0 TDS but phosphate detected

balix · Mar 6, 2016

I have a BRS RODI unit. It's producing 0 TDS output but my Red Sea test kit is detecting 0.08 phosphate and confirmed with my API test kit. Using this water to top off and for water changes. It's zero TDS since the phosphate is under 1 ppb.

I just changed the sediment, carbon, DI resin and membrane.

Would adding on another deionization canister help? Or any other suggestion.

Salt Creep · Mar 6, 2016

How old is your tank? PO4 can leech from your rocks for months if you have un-cooked/cured live rock. Did you use dry rock? 0.08 isn't terrible... are you having algae issues? I don't even use PO4 tests because a lot of it is locked up in algae and the test isn't really a true representation of how much you have in your tank. This is something I feel you can gauge just by looking at your tank.

AZDesertRat · Mar 6, 2016

You cannot accurately test phosphates or any other single analyte in ultrapure waters without the use of lab grade instruments. Hobbyist grade test kits will not do it. Your best bet is a high quality ATC handheld TDS meter such as the HM Digital COM-100 which tests both electrical conductivity and also TDS down to tenths.

balix · Mar 6, 2016

AZDesertRat said:
You cannot accurately test phosphates or any other single analyte in ultrapure waters without the use of lab grade instruments. Hobbyist grade test kits will not do it. Your best bet is a high quality ATC handheld TDS meter such as the HM Digital COM-100 which tests both electrical conductivity and also TDS down to tenths.

This is after mixing a new fresh batch of saltwater (red sea pro). I did test the water itself. Not concerned with the TDS but rather the phosphate. I have my unit at 80 PSI with booster pump. Wonder if slowing that down a bit might help.

Bunnee911 · Mar 6, 2016

What is the phosphate reading from your aquarium? A little is actually OK..

AZDesertRat · Mar 6, 2016

Most salts contain traces of phosphates, in small amounts like that it's nothing to worry about.

RO membranes are more efficient at higher pressures, reducing it would be counterproductive.

balix · Mar 6, 2016

Salt Creep said:
How old is your tank? PO4 can leech from your rocks for months if you have un-cooked/cured live rock. Did you use dry rock? 0.08 isn't terrible... are you having algae issues? I don't even use PO4 tests because a lot of it is locked up in algae and the test isn't really a true representation of how much you have in your tank. This is something I feel you can gauge just by looking at your tank.

Tank is just about a year old.

Bunnee911 said:
What is the phosphate reading from your aquarium? A little is actually OK..

Tested my RODI water and after mixing it with salt. Phosphate detected.

phosphate in tank is a little less than 0.08. I'm trying to achieve 0.03 but I feel like my top off and water changes are keeping it at 0.08. I know I shouldn't try to chase numbers but my corals frags are okay at best and not opening like it did before.

I have two tanks.

20 gallon - just started biopellet about 2 weeks ago.

10 gallon - Started NOPOX a month ago and seeing a slow but good decline in nitrate but nothing has changed with phospate around 0.08.