API PO4 Test kit problem

[Fazulka]

I bought the API phosphate test kit. I wish I had sprung for something better. API is just so familiar and I have lots of those little vials!

Now I can't tell what reading I am getting. It looks like 0, 0.25, and .5. Why is 0 darker than .25? It makes no sense.

Any suggestions other than just biting the bullet and buying a new test kit?

 

[dwd5813]

i've read that the api kit has some accuracy issues at low levels. truth be told, i don't test phosphate anymore since if there is any it's going to feed algae and make a test read low/0 anyway. i let algae growth in my tank tell me about the phosphate in the system. if you want to test i would bite the bullet and go with a better kit. i'm sure someone around here will come along with a good suggestion on which one to go with.

 

[rgrobe]

Po4 test kits are usually not accurate at the low levels really required to make a difference. The API kit will measure .25 or .5 but the fact is that you are shooting for <0.05 to reduce nuisance algae. I have heard that the Salifert Po4 test is fairly accurate although not at the very low desirable ranges.

I switched to a Hanna phosphate photometer which allows me to maintain a 0.02 to 0.03 range consistently.

 

[PRDubois]

To check phosphate I take a sample to my LFS and let him use his meter.