A good investment might be your own test kit for the future.
I use API liquid for ammonia, nitrite, nitrate and ph. For the more sensitive tests like calcium, magnesium, phosphates and alkalinity I use salifert test kits. A bit more money but always right on the money as far as results. I;ve used the API phosphate test and come up with none and then the salifert and have come up with a reading so depending on the test your lfs
uses you might have a higher reading in reality.