Should I get the Phosphurous Checker?

[Wheelman76]

I should have mentioned that I'm really carefull that I wipe all the fingerprints off the vial in between all the steps of the test. I'm not sure if that would lead to inconsistent readings that people are getting or not?

[lastlight]

yes i didn't mention that as i assumed everyone would be doing that already but for sure it makes a difference.

[Fishfriend]

I have a hanna phosphorous checker that I can sale you for $20. I am getting out of the hobbie.

[asylumdown]

Part of me wonders if it's the units themselves then, because people who can't seem to get consistent results never do, while the other camp never seems to have problems. I actually have training in analytical methods and have spent an unfortunate number of hours in a soil and water lab, and I still can't get mine to work properly.

I had a period where I thought my tank was melting down because every week I'd test 0.03-0.08 ppm higher than the week before - even with fresh GFO, and even while dosing lanthanum. Converted to ppm, I was reading in the 0.3 range.

Then i did a sequence of tests back to back in one sitting. The levels rose by 0.03 to 0.08 with each sequential test! the reading was predicted by the total number of tests I had run in that vial, not the level of phosphate in my tank.

I did the acid wash (which melted the max volume marker right off), then did a dummy test with distilled water and still got a reading of like 16 ppb or something.

I promptly drove to Wai's and bought a regular PO4 kit. That appears to have solved my phosphate problem, as my readings have been 0.00 ever since

[lastlight]

the Lastlight Checker Holder© is fully compatible with both Hanna models. comes complete with removable and washable funnel.

[asylumdown]

Brett, there are times when life gets busy and I get all distracted, and just for the tiniest moment I forget that you're my hero.

Then you remind me.

[tytown]

Ok, feeling better about it tonight. I went at it again but with the approach based on people's comments and some other research and was able to get a spread of readings within the units rated accuracy +-0.03 ppm (+-5% of range; range =200 PPb)
I perfectly prepped the reagent packet to ensure that it would all get in the vial before the test is even started
Grabbed water from the same location in the tank being careful not to get finger water in the sample.
I kept the orientation of the vial the same throughout all tests (10ml facing me)
And I used a fresh microfibre cloth and meticulously buffed the outside of the vial.
After all that it tells me I have 0.09 - 0.12 ppm PO4.
I would have liked to know which of the above had the largest influence on the results and I wonder what my readings would have been if the vial was flipped 180. Unfortunately I can't debunk the errors I went through becuase I only have 4 reagent packs left from my box of 25 bought just yesterday.
I'll use the current levels as a reference from here on out.
Thanks everyone.

[asylumdown]

If you have access to one, might be nice to test with one of the PO4 hanna's as well. The other thing I would find is that my ULR kit, when converted to ppm, seemed incapable of returning a result much below 0.08, while the regular kit would return 0.00.

If both the regular range and ULR kits agree that your PO4 is in the 0.09 to 0.12 range, then your method probably worked and you can have a higher degree of confidence in your results.