Over the past several weeks, I have been testing my pool water by three different approaches: 1) the TFT kit, 2) the ColorQ 7 system from LaMotte, and 3) the Bioguard Alex system at my neighborhood pool store.
My pool: 35,000 gallon, pebble-tech surface, DE filter, chlorine generator.
Below are the results of my two most recent tests (sorry for the formatting, I couldn't figure out how to do tables.) The first column of results is from the TFT kit (ordered from http://www.tftestkits.com/). The second column of numbers are results from the ColorQ system, and the third column is from the computerized, Alex system at the Bioguard store.
TFT ColorQ Alex/Bio
FC 0.5 0.44 0.1
CC - - -
TC 0.5 0.45 0.1
PH 8.2 8.30 7.3
TA 140 80 188
CH 190 191 200
TFT ColorQ Alex/Bio
FC 1 1.36 1.3
CC 0 0.3 0.2
TC 1 1.66 1.5
PH 7.6 8.0 7.3
TA 130 88 147
CH 200 174 203
I follow the prescribed procedures for the TFT test, rinsing the vials with pool water before filling to the appropriate levels. For the ColorQ, I rinse the test tubes and fill to the appropriate levels, add drops, shake and measure in the order prescribed the the instrument (I don't wait long between shaking and measuring). For the Alex, I stand around and wait while the measurements are taken (pretty boring, not nearly as fun as doing it myself.)
I'm pretty comfortable with the FC, CC and TC values - they seem to be consistent across all three tests.
I'm uncomfortable with the other values (pH, TA, and CH). There seems to be too much disagreement between tests. In any case, results of these tests recommend different chemical applications, often in opposite direction.
Questions for the group
1) Would the high salt levels account for some of the test differences?
2) Does the temperature of the water affect the results?
3) Any suggestions for improving this situation?
4) Which test should I "believe."
Inquiring minds (at least mine) want to know! Thanks in advance for your insights.