Using a floating feeder with tablet chlorine or tablet bromine will cause even a great cover to begin absorbing water - or gaining weight through osmosis I guess...
Also, I saw somebody mention above: when you add chlorine or MPS you should run the jets with the cover open for awhile. "Awhile" is defined like this: the longer the better - until there is no chlorine odor coming off the water is best.
I use a floating brominator with a few tabs (5 little ones) with the opening in the floater minimal (even with that few tabs and little flow the tub smells like bromine) and throw in some "fresh and clear" (shock) after a large group of people are in the tub. Would you suggest another method?
What is MPS? Also, as long as the chemical is in the water wouldnt the odor be evident?