My dermatologist confirmed my skin allergy to MPS. I was the only one in my family to experience the large red bumps on arms and legs. The tub (400 gal.) was drained - filter cleaned with Aqua-EZ (great product - removes iron and clarifies water instantly!) - and tub then refilled using Dichlor only and new mineral cartridge. It worked - no more bumps. Here's the issue - my son put in 2 tbls of the old shock cleaner with MPS the other night after he left (yes, I should have thrown it away). Took a tub last night - the bumps reappeared this morning - I asked him what he added and he confirmed it was the older bottle of shock. So - my question is - will just a few tbls. of MPS wear out if I leave it for a few days? If I add more dichlor will that burn it off? Or - do I need to drain and refill tub again? Thx in advance!