RODI water = 0.35 ppm phosphate ?

[satbert]

My tds = 0 but my rodi water is 0.35 ppm PO4 measured with Hanna checker. Does it mean my RO membrane needs to be replaced or that I need to change the DI resin ? What else to look for ? Now I understand why I can't get my PO4 down in the tank water ! The RO membrane is about 3 yrs old, filters and carbon cartridge changed every 12 months & I make about 5 gallons of water per week.

Tks for your help !

 

[Luukosian]

Think you answered your own question there....if your membrane is about 3yrs old it probably needs replaced. Any part of the system you can eliminate as the source of the problem will get you closer to your answer.

 

[steved13]

Phosphate is an Ion, I would suspect the DI resin.

 

[satbert]

Thank you both. For what it costs I'll replace both the DI resin and RO membrane. Otherwise it is just futile to try and combat PO4 in the tank.....

 

[steved13]

good thinking

 

[Fishwhiz]

The DI resin is not used up unless its gold amber. If the membrane went bad, you would be getting improper ratios of waste to product.

 

[magnetar68]

If you find the issue is not with the RO/DI water, make sure the vial is very clean. I have found the Hanna checker very sensitive to oil on your hands. The vials must be very, very clean. I don't touch the vial with my hands. I use an optical cloth whenever I touch it and try to hold it by the cap.

 

[Boomer]

RO membranes can last for years. Second, I do not trust meters, such as the Hanna in RO/DI water. Third if you have zero TDS that PO4 reading is off.

 

[ChrisY]

Boomer I agree. if TDS is zero then either it is wrong or the Po4 test is wrong. are these both tested in the RO/DI water coming out or after its in tank?