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High PO4 in RODI water?

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Hi everyone,

I recently got an ICP kit from icp-analysis. It included two vial so I decided to send in a sample of my tank water and the RO water I usually get from RiverCity Aquatics. I got the results back today and to my surprise, the Phosporus was 0.16ppm (tank water) and 3.37ppm (RO water). That's not a typo. I shows 3.37ppm.

I have been trying to get my PO4 lower in my tank but did not even think it could be coming from the RO water. Could the water from RCA be this bad?

I don't have an RO/DI system so I have been relying on water from RCA for water changes and top-off. This is very concerning.

The tank is an IM 20 peninsula. I change about 10-15% weekly and don't feed an excessive amount (2-3 times a day but just a pinch or a little frozen each time). I have been putting in GFO for 24 hrs, test and remove it. It would go down but would immediately start creeping up when I check again after 24 and 48 hrs. My PO4 is around 0.9 according to the Hanna checker. It would go down to about 0.65 after 24 hrs with GFO. Once I remove the GFO, it would slowly start creeping back up...about 0.1 each day.

Aside from getting a RO/DI system, what are my options at this point?

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Well, obviously your tank is using a lot of phosphate.   :smile:      If it's just RO water a lot of thePO4 in the tapwater will make it through the membrane.  It needs to go through a DI filter to remove the all of it.  And even if all the PO4 is removed, If it's stored in a container there could be increased levels just from dust and stuff in the air or bugs getting into the storage tank.   Which also raises  the question of what might be in your containers?   Also keep in mind ICP tests have an element of error, see Richard Ross' article on comparing ICP to a Spectragraphic analisys.    And here's a link to my post on ICP results for a system maintianed with tapwater  if you want to compare results with another test.  And to help add some perspective on "acceptable" PO4 numbers here's and article showing increased growth with increased PO4 as well as Richard Ross' video on PO4.   And if you want to dig into the issue a little deeper there's this research done by the University of SOuthampton on aquaria maintianed corals:


An Experimental Mesocosm for Longterm Studies of Reef Corals


Phosphate Deficiency:
Nutrient enrichment can increase the susceptibility of reef corals to bleaching:

Ultrastructural Biomarkers in Symbiotic Algae Reflect the Availability of Dissolved Inorganic Nutrients and Particulate Food to the Reef Coral Holobiont:

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates



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