I just noticed this and I'm curious as to why there is a difference. I noticed my TF-100 test kit has recommended TA levels for non-salt 100-120, but the recommended levels for TA in Pool School for non-salt (bleach) is 70-90+. Why the difference? Wondering where the best TA range would actually be for my vinyl pool, 70-90+ or 100-120? Mut be missing something here. Must mean ranges from 70 to 120 are acceptable?