pH, Free Chlorine and Total Alkalinity Sensors pH, Free Chlorine and Total Alkalinity Sensors mechanicalchad (Mechanical) (OP) 26 Feb 18 00:40 Looking to play around automating my hot tub chemicals. Does anyone know of good, cost effective methods to sense pH, Free Chlorine, and Total Alkalinity that would give a 4-20 mA Output? Thanks, Chad RE: pH, Free Chlorine and Total Alkalinity Sensors djs (Electrical) 1 Mar 18 18:50 pH is no problem. FC and TA are another issue. If you are not using CYA in the hot tube you can use an ORP probe to measure the free chlorine. To the best of my knowledge there are no TA probes, most TA instrument rely on titration. In any case any of these options are not cheap. The pH and ORP probes will probably run $1000 to $1500 each. RE: pH, Free Chlorine and Total Alkalinity Sensors mechanicalchad (Mechanical) (OP) 4 Mar 18 21:41 Awesome thanks! I'm thinking I should be able to infer alkalinity based on pH changes after adding acid and corroborating with some manual measurements at the beginning. Good enough for what I'm using it for anyways. Do you happen to know of any good brands for pH and chlorine? Thanks again!