Quote Originally Posted by Simmons99
Holy cow - If I understand your post you are stating if you had a CYA of 100 - you would need to shock to 50ppm (poor vinyl liners )?

Personally - I would try the Best Guess Chart first and then raise 5ppm a day until I saw some progress if needed.
Your pragmatic and safely incremental approach is certainly the way to go. We're not officially changing Ben's chart just yet (only Ben can do that and only after real-world experience bears this out), but it may very well be true that to get rid of algae quickly, a shock to 50 ppm FC is needed when the CYA is 100. HOWEVER, keep in mind that 50 ppm FC isn't really as high as it sounds when there is CYA of 100. IF what damages vinyl liners is the oxidizing and disinfecting form of chlorine (HOCl), then this level is only 0.5 ppm which means that as far as the vinyl liner is concerned, it is being exposed to exactly the same amount of chlorine as if it was 1.0 FC with no CYA (assuming half is HOCl at pH 7.5).

Again, this is speculative "theory" at this point, but the more evidence I see, the more I'm thinking it's true.

Richard