I'm having troubles getting and keeping my hot tub water clear since the spring. I typically replace the water and filter in the hot tub twice a year (May and Nov).
I emptied the hot tub on 4 May, cleaned and rinsed the inside, blew as much of the water out of the pipes as I could with the exhaust side of a 6.5hp shop-vac and vacuumed up any water so the inside of the hot tub was dry. I replaced the filter and refilled with tap water and added chemicals. I use the chemicals recommended by the place I bought the hot tub (sodium dichlor 99% sanitizer by SpaGuard or BioGuard, Rendezvous Activate <Potassium Peroxymonosulfate 32.18%>, Rendezvous Protect Plus, and Rendezvous Natural Clear Enzyme Clarifyer). They recommend adding 4oz sodium dichlor once a week, 4oz Activate once a week, 2oz Protect Plus once a week, and 2T Natural Clear once a week, each chemical added on a different day. I still use these chemicals because I bought a lot of them over the winter before I found this site. I want to use these chemicals up before I switch to the BBB method recommended here.
The hot tub water was fine for about 2 weeks. My 16 yo son and a bunch of his friends came over to use the pool and hot tub and 2 days later, the water in the hot tub was cloudy and foamy (water in pool was and continues to be fine). I used Foam Out and tried shocking the water but that didn't help. So I emptied the hot tub, cleaned everything out again, but did not replace the filter as it was only about 3 weeks old and cost $180 (I did remove the filter, rinse, and let dry outside the hot tub). Refilled with clean water and added chemicals. By the 2nd weekend in June and limited use, the water was cloudy and foamy again. I used Foam Out again to get rid of the foam and started using the Natural Clear stuff every day but if I missed a day, the cloudy water and foam came back.
I'm not sure what's wrong with the water. The first bout of foam could have been residual laundry detergent in my son's friends swim suits though I thought replacing the water would clear that up. Some of the research I've done indicate this could be high TDS but I thought that was an issue that occurs over a long period of time. The water in the hot tub has only been in the tub for about 5 weeks now. The foam does leave a yellowish scum at the water line especially in the filter well; the scum cleans up relatively easily with a towel soaked in Natural Clear.