After attempting to resolve the high phosphates readings in the tank, I believe that the water quality may not the issue after all. Replacing DI resin, letting the filter run for an hour and retesting the rodi water got my hanna checker register 0.18 ppm of phosphates. There was clearly something wrong, then I remembered that I have some distilled water, which is supposed to be free of any impurities. The distilled water test came back at 0.10 ppm.
To summarize, my phosphate readings on all sorts of water samples were all over the board lately. I have two different sets of reagents showing same results. Now there could be four plausible scenarios here:
- All water samples, including distilled water, do in fact contain phosphates
- Digital Hanna Checker is malfunctioning
- Both sets of reagents are no longer good
- Operator error
Issues with the operator are highly plausible, after all he is getting old. But that same operator conducted several dozen tests already just trying to find a solution to the problem. Making errors in all tests is unlikely. Having another checker to test against would have taken care of the second scenario, but I don’t have another checker. I could validate the quality of reagents with a phosphate test of a different brand, like Salifert, but I don’t have it either. Finally, I could take my water sample to an LFS nearby and have them test it, but I doubt they would have equipment precise enough to give me a reliable answer.
Next step to call Hanna’s tech support and see what they have to say about this.