Your help regarding reading the results from an API liquid phosphate test kit please! A picture says a thousand words so:
As you can see, my test tube is a light yellow colour, but the freshwater colour chart goes from light green to dark green. I take it that this probably means 0 ppm phosphate, but the chart shows that even a zero reading should give a light green colour, not yellow. However, on the saltwater colour chart (the water sample is from a freshwater tank, not marine!), the zero reading is actually supposed to be yellow:
So what on earth is going on here? Any ideas please? I'm pretty experienced by now with using these test kits and have followed the instructions to the letter:
I have also tried adding a drop of Seachem Phosphate into the test water and confirmed that the test tube does go a dark green colour, so I don't think it is a faulty test kit. Expiry in 07/2022 so not out of date. I know some people report faulty test kits, but I'm also aware that user error is far more likely. But I can't see what I could be doing wrong? I've done 20+ tests now on 4 different tanks and pretty much always get the yellow result. I did overdose* a tank I was cycling on one occasion and that's the only time I got a hint of green.
*compared to my usual dosing which is around Seachem's recommended 'beginner' dose
Why is my reading yellow and not light green as per the freshwater colour chart?
Is it just because the API test kit has such low resolution at the low end? Does anyone else get similar results? I am doing something stupid?
Ideas please! Thanks, James