Two vastly different po4 readings, opinions please

[George81]

So I purchased a salifert po4 test kit which got delivered today. My other test kit is Red Sea. It expires this month.
my salifert test kit gave me a 0.5 ppm result 3 times.
my Red Sea which has consistently given me the same reading is between the 0.08-0.12 Colour range. So I’m guessing I’m at 0.1
which result do I go with. I have very minor algae growth on the gyre covers. Nothing major. thats the only spot I see algae.
the tank has been set up since late jan or early feb of 2019. with dead live rock that I bleached. the Rock was stored for 12 years from when I shut my tank down in 2007.

i Recently added cheato back into my fuge. I’ve had it for about 3 weeks. There is little growth.
i carbon dose 120ml of vinegar in my tank daily. Recently added a brightwell brick. And microbacter7.
other parameters
nitrates 5-10 Red Sea and salifert
kh 8.3 salifert
ca 430 red sea
mag 1360 red sea
sal 35ppt refractometer
ph 8.15 salifert.

I have a copper band butterfly so I feed frozen exclusively . 2 cubes daily that I don’t rinse. I added phosgaurd today to my carbon reactor. But prior to this I hadn’t used any phosphate removal for well over a year.

any thoughts or input on which reading I should go with. Or should I not care. Is 0.5 a high reading I have mostly sps that seem to be doing ok.

 

[Shirak]

Just chiming in that you are reading the Salifert test correctly. I don't have the PO4 one but from my experience with some of the others you need to be sure you are reading the amount remaining in the syringe, not the other way around like most other test kits.