can't get chlorine reading

[garedm]

chlorine level dropped out from 756 down to 365. keep adding chlorine but when i reach 700+ by morning its dropped out again. Ph levels are steady at 711. Its an automated system. Test kit shows perfect ph but shows clear for chlorine HELP

[chem geek]

I presume you are giving ORP readings in mV, is that correct? Chlorine and pH are not measured in units like 700 or 711. You've got something consuming chlorine or your automated system isn't outputting enough chlorine. See if the problem only happens during the day. If so, then if the pool is exposed to direct sunlight, you may not be using any Cyanuric Acid (CYA) and that is allowing chlorine to get broken down too quickly by the UV in sunlight. With an ORP system, you can't use too much CYA, but 20-30 ppm should be OK. However, you will likely have to readjust your setpoint since with CYA your ORP will be more like 650 mV or so.

If you are losing chlorine even at night, check the level using a test kit and see the FC loss in ppm overnight. You might have a nascent algae bloom in which case you need to shock the pool with chlorine -- do not rely on the automated system to do that as they usually cannot keep up with algae growth once established.

Did this problem happen all of a sudden? Is this only during spring opening?

[Guest]

You need to shock the pool with non.stabilizer chlorine. Then shock again and again until the chlorine doesn't fall any longer.