I personally recommend the salifert kit, I think it will give you the most accurate PO4 readings. However, you can always ask your LFS to test it for you. I know our stores around here us a Hanna for their test, which is extremely accurate. Someone around you may do the same. Anything below .1 would be good. Anything below .25 is acceptable. And anything higher will really restrict your coral growth and survival. You can always do a series of small water changes ( less than 10% total water volume) over the next couple days and see what the results are, that will certainly lower any PO4 in the water, and may provide relief.