Friend of mine is running an apartment pool, which is a sparkling oasis... That said he knows he needs to drain some water because the CYA is high (slightly over 100). It is 70000 gallons and chlorinated with Trichlor pucks on two feeders. Two sand filters run 24/7. It gets Backwashed once a week swapping around 600 gallons.
He keeps chlorine around 7.5 ppm on the Taylor 2005c comparitir using the standard DPD test.
There is no combined Chlorine that we can tell as it does not get darker when adding R-0003.
CYA 110 hard to tell
He has a $400 a month budget for chemicals and management refused to allow a liquid chlorine pump because it goes over budget. He cannot add any chemicals at all during the day or when people are in the pool.
Looked into cal hypo feeders, but it is like $2000 for proprietary cal hypo feeders and cal pucks that cannot be fed in a Trichlor feeder. Again not an option.
He did buy a bucket of cal hypo 48% grainuals... Unopened.
Last night he put in about half gallon of 31% acid and nearly half a gallon of Polyquat 60 as a preventative.
State is GA and the Heath Dept. requires between 5 and 10 ppm FC, but he is not certain this will sanitize the pool at this CYA.
What can be done in the next couple weeks to keep it open and sparkling clear. He cannot drain any water for the next two weeks.