I have a new tank (240 gallons, 350 gallon system), that I'm dosing phosphate to. To get the dosing dialed in, I've been monitoring phosphate daily with the Hanna Phosphorus ULR checker. After several days of unexpected results, I decided to try to see if the results I was getting were repeatable. They are not. For example, yesterday I repeated a test three times, and got phosphorus readings of 50, 68, and 105 (corresponding to phosphate readings of .15, .21, and .32). With this level of inconsistency, it's tough to accomplish what I'm trying to do! Here's my process:
* Before and after each reading, I half fill the vial with aquarium water, put the cap on, shake vigorously, and dump it out.
* I fill the vial using a graduated syringe, so more accurate than trying to eyeball the line on the Hanna vials.
* I use a magnetic stirrer to stir the vial for 3 minutes. (And I put the stirrer in the vial when I rinse it.) (And I use the stirrer only for this checker.)
* I am careful to get all the powder into the vial, and I don't touch the inside of the envelope.
* I carefully wipe the vial with a paper towel.
* I even line up the vial the same way when I put it into the checker.
Today I tried something different. I first filled a vial with aquarium water, and put it in the checker for the "C1 test". I then used a different vial for the testing solution. I repeated this 4 times, using the same vial for the C1 test, and using the same vial for the C2 test without remixing more reagent. Before each C2 test I stirred the vial for a minute, in case there had been any precipitation. So the results should be the exact same each time, right? No! I got readings of 60, 76, 0, and 0. So why would it go down to 0? Does the solution turn back to clear after time? If so, then it seems like the timing of how you run the test would be critical, even though the instructions are pretty vague about that. And if that were true, why would the second reading be higher?
Any suggestions would be much appreciated. Maybe I have a bad checker?
* Before and after each reading, I half fill the vial with aquarium water, put the cap on, shake vigorously, and dump it out.
* I fill the vial using a graduated syringe, so more accurate than trying to eyeball the line on the Hanna vials.
* I use a magnetic stirrer to stir the vial for 3 minutes. (And I put the stirrer in the vial when I rinse it.) (And I use the stirrer only for this checker.)
* I am careful to get all the powder into the vial, and I don't touch the inside of the envelope.
* I carefully wipe the vial with a paper towel.
* I even line up the vial the same way when I put it into the checker.
Today I tried something different. I first filled a vial with aquarium water, and put it in the checker for the "C1 test". I then used a different vial for the testing solution. I repeated this 4 times, using the same vial for the C1 test, and using the same vial for the C2 test without remixing more reagent. Before each C2 test I stirred the vial for a minute, in case there had been any precipitation. So the results should be the exact same each time, right? No! I got readings of 60, 76, 0, and 0. So why would it go down to 0? Does the solution turn back to clear after time? If so, then it seems like the timing of how you run the test would be critical, even though the instructions are pretty vague about that. And if that were true, why would the second reading be higher?
Any suggestions would be much appreciated. Maybe I have a bad checker?
