Strange- chlorine seems to be increasing overnight

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
New to me pool, built in 2005. Water is clear. A little bit of green around the water line at the skimmer opening. Previous owner was using solid chlorine tablets. I switched to liquid until I can get a SWG. Passed OCLT about a week ago.

Current test results:
FC 11.5
CC 0
pH 7.5
TA 90
CH 330
CYA 80

The strange thing... I haven’t added chlorine in a few days and it hasn’t been dropping. It was 10 last night and 11.5 this afternoon without adding anything. :confused: The chlorinator is empty. I removed the floater, which was also empty. I am keeping a solar cover on when we’re not in it but I would still expect some chlorine loss just from all the pollen dropping right now.

Any ideas? My test reagents aren’t that old but I was planning to buy all new when he has the annual preseason sale.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
It was 10 last night and 11.5 this afternoon without adding anything.
Well, one thing for sure, FC won't increase on its own unless there's some tablets or automated additions of chlorine. Since you don't have any of those, I suspect the odd increase is attributable to the before & after testing. Maybe the pump didn't mix the water well enough at one point, or perhaps the water sample was from a different area? Of course there could always a slight FC variation in the test itself. I'm assuming with the TF-100 you're pulling a 10ml water sample, adding the powder, then counting the drops until clear and dividing by 2? Example: 20 drops = FC of 10. If there's something else we should consider let us know.
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
Yep, that’s how I’m doing the test. The water samples may have been from different areas and the water might not have been circulating every time I took a sample... didn’t think of that. I will try to be more consistent. :cool:

Doing another OCLT tonight. First quick dip in the new pool was yesterday. Vacuumed and scrubbed the waterline today. It’s looking good!