OCLT is best done at elevated FC levels. If you want to be extra sure, use the 25 ml sample and get .2 resolution on the FAS-DPD test.Ok, we don't have any lights and we haven't installed the ladder since we open the pool this "spring" ( it keeps turning back to winter weather every other week here in SC) so there's is really nothing in the pool but water. Can i do the overnight loss test tonight or do i have to wait until the fc levels drift down?