Phosphate in food

[MitchM]

Seeing as how P04 levels in our tanks seems to keep creeping up, I tried a test yesterday to see how much is in the food that we are feeding the inhabitants in our tanks.

I took a single 7 1/2 x 8" , 2.8 gram piece of nori and placed it in 1 liter of RO/DI for 24 hours at room temperature and tested the water before and after.

Before P04 was 0.0 ppm.
After P04 was 1.0 ppm.

The only nutrient export systems that I am using are protein skimming and water changes, which are not enough as I am seeing more cyano growth and small patches of hair algae appearing.
I would like to get some macro algaes growing, but my sump and main tank have large algae eating fish in them, most of which are being transferred to a new system soon.
I'm looking forward to seeing if planting some macros will work to take up the P04 fast enough to compensate.
I measured my tank water and it showed 0.5 ppm P04 before the water changes that I am now doing.
I'm going to do the same test with some frozen mysis, rinsed and unrinsed next.

edit:
18 grams (about a tablespoon) of Piscine mysis, unrinsed, showed about 2.0 ppm in the same test.

edit:
18 grams of frozen mysis, thawed then rinsed briefly in R/O brought the weight down to 14 grams. P04 was a little over 1.0 ppm.

Mitch