What is the cyanuric acid or stabilizer level? That could have a lot to do with it. Also, not sure what part of the country you are in, I’d drain some water and add fresh. Also check where you are buying your tablets? We’ve always recommended purchase only from a reputable pool store, big box stores aren’t reliable sources of chlorine as their quality greatly varies and depending on their country of origin often have much more additives in them to create the tablet form.