Phosphates in fresh saltwater

Ok so I was having a algae problem in my tank and am paranoid. So I decided to test my fresh saltwater (red sea pro test) and it had po4 in it about .23 is what it looks like. So I switched my membrane in my ro/di changed my pre filter, carbon filter and resin dual DI. My TDS out says 0. I went to home depot purchased 2 brand new rubbermaid containers, and have switched salt from esv to tropic marin and still have the same results. Could I be getting a false positive with my test kit? or am I missing something?

 

I would guess it's your test kit. Which one are you using?

 

Im using the red sea test kit
Reef Care Algae Control Multi Test Kit - Nitrate and Phosphate - 100 tests | Master Test Kits | Test Kits & Refills | Aquarium - ThatPetPlace.com

 

The chemicals in test kits do get old and are the main reason for false positives. I would at least take a sample to the LFS and see what their results are. Neither of those salt mixes should have phosphates.

 

the test kit is not that old only 3 months from manufacture date but i am going to the lfs today

 

So looks like it was the test kit I had a friend test with a Hanna checker it came in at 0 thanks for the help all I will not be getting any more red sea test kits. It was all but brand new.