Some imporant tips for accurate testing with the Hanna Phosphorus Checker:
1. don't fill the vial with a syringe, dip the vials directly into the water to fill for the Phosphate tests. This isn't needed for the other checkers, but the syringe may have residue that effects the phosphates. I noticed if I use my feeding syringe the fill the vial, it tests off the charts.
Actually, it's best to use a clean syringe to fill the cuvettes (plural, yes). I keep a dedicated testing syringe; the only it sees is pure tank water. Certainly using a dirty or food syringe will give you false positives. Relying on the line printed on the cuvette is not preferred, as it isn't necessarily an accurate measurement either (position of the line, variation in the glass thickness & shape, etc).
2. After putting the water sample in the vial, wipe off the glass and don't touch it anymore. Always wipe it down between phases.
Yes! Finger prints, or excess lint, on the cuvette can skew the test results. Use a lint-free cloth to wipe them down well before placing them in the checker.
3. Align the vial the SAME way as you calibrated it after adding the reagent (I keep the "10ml" writing facing perfectly forward)
This shouldn't make much difference, but might. The pickup in the checker is intentionally below the markings on the cuvette.
4. After you shake the heck out of the sample after adding the reagent, before putting it back in the checker slowly swirl it and invert it to remove any microbubbles off of the glass. All of the reagent WON'T dissolve. Shake very quickly for about 60 seconds and slowly swirl and invert for the next 30 seconds. This will give you 30 seconds to clean the glass and re-align the vial in checker.
Yes, bubbles will skew the test. But the reagent SHOULD be entirely dissolved.
Use both cuvettes for every test. Use one as the reference (C1) and the other then as the sample (C2).
Fill them both, and dump in the ENTIRE contents of the reagent pack into the C2 cuvette. Put the lid on and shake it VERY well, until the reagent dissolves entirely. Then wipe both cuvettes clean on the exterior with a lint-free cloth. Now before placing either of them in the checker, tap them repeatedly (I tap them gently -they are glass after all- on the counter-top) until ALL the micro-bubbles have released to the surface. Now start the test with the reference (C1).
5. Finally, instead of just pressing the button to get the number instantly (after C.2), hold the button down until a timer appears. This gives the sample time to settle out and the results to be accurate. The timer is 3 minutes and will give you the reading after the countdown is over. I tested this and the results with no timer vary wildly. With the timer, results were consistently +/-2 ppb of my 8ppb levels between multiple tests. Without the timer, they were always extremely high, and all over the place, up to +20ppb, resulting between 15ppb and 25ppb when in actuality they were 8ppb.
Yes, you have to hold the button after placing the sample (C2) in the checker.
Also, instead of just multiplying by 3 to get your phosphates from the phosphorus reading, use the actual equation: [HI-736 Reading] * 95 / 31 / 1000 = PPM Phosphate
The equation is equivalent to multiplying by 3.066 and then dividing by 1000 (ppb to ppm). So multiplying by 0.03066 is mathematically the same thing.
Also, the HI-736 is by far the most accurate hobbyist colorometer of any sort on the market - compared to several thousand dollar lab equipment, it spot on. That can't be said for their Alk checker, but that is at least extremely consistent between tests and the error is always the same between tests. And the Ca checker is a complete waste.
Gonna try to test tonight and subsequent days. I followed instruction to a T but yea, you only get two min before the checker timed out.
