Question about Hannah checkers

[FragIt Dan]

PO4 is good, Ca can be good but the syringe they give you to add 0.1ml of tank water is, IMO, not accurate enough. I carefully did several tests in a row on the same water and had readings fluctuating by 40-60ppm. I eventually got a very accurate glass pipette and am getting much more accurate readings. As already mentioned, you need to use very clean RODI water as part of the test, but you can verify it is Ca free by running a test without adding any tank water and dividing the test result by 100; ie if you do this and get a result of 200, your RODI water has 2ppm Ca in it. You should/will need to get a reading of 0, indicating a result of 0.00ppm, if it is flashing 600 then you have more than 6ppm Ca in your RODI water. If you don't have access to good RODI water, go get a 4l jug of distilled water from a pharmacy (~$3) and run a test on it to make sure it's ok.
Dan