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If you drain it, make sure you use a shop vac to get all water out of the lines. Otherwise the stagnant water will go bad. Also an empty hot tub in the hot sun is not good for the shell.The vanguard, has a circ pump, daily filtration and and ozenator. I would shock the tub, put in some dichlor and not worry about it.You mentioned you use dichlor everyday. Is this because you use the tub everyday? I would only use the dichlor after the tub is used. There is not need to be adding dichlor every day unless you are introducing bacteria into the tub (IE using it).