I start flushing wen the thricomes ( you can check them with a jewelers loop) are turning cloudy and harvest when a 5/10% of them are amber ( on the buds ) .
Flora kleen or every else flush product you can use it for sure the first heavy flush so it can suck all the salts in the runoff water, then u can use it the next week if the salts level are uet high or you can only continue the flushing process with only water and maybe a little bit of molasses to get the best from your crop! Your plants look healy and near the flush!
If you have not or are not planning to buys a jewelers loop now , i suggest u to star flushing now and harvest in like 2 week +-