Phosphates in RO/DI Water

[BigHildy53]

My tap water starts at 1.3 mg/l of phosphate. I have a seven stage RO/DI system; with a booster pump. One sediment, two carbon, two RO membranes and two DI. I've replaced everything except the RO membranes. The water being produced is down to .6 mg/l of phosphate.

Is a .7 mg/l reduction is phosphate "normal" or within expectations for an RO/DI unit?

 

[Travis Stewart]

Following

 

[BigHildy53]

I keep my water in a 100g vertical tank container in the garage. I've hooked up a pump and media reactor filled with GFO. I pump the water through the reactor and back into the tank. After several hours, testing the water coming out of the media reactor reads zero phosphates.

 

[PatW]

Cycling through GFO is one to handle it. But I thought that the RO membrane should reject about 98 percent of the stuff. You are observing only a 50 percent rejection. But I am not an expert on RODI. I am hoping that someone who is will chime in.

 

[BigHildy53]

I thought that Phosphate was removed in the DI resin. But I've ordered replacement RO membranes just the same.

 

[BigHildy53]

My RO membranes were spent. They were only replaced in early October. But my guess is that the couple of times I let the unit run much much much longer than it should, probably negatively impacted things. Teaches me to be more vigilant about testing the water on a monthly basis.