What causes a yellow scum build-up in a hot tub?
"I test my water daily and adjust when needed, but I get a yellow scum build up when the jets are on high (above water line) It is quite thick and on the cloth it looks brown. I wipe it off - have used a clarifier and it really foams and the scum appears, I wipe it off and it is good for a few days but comes back. I have tried descummer (the 3 separate doses as recommended - the scum comes back. I have shocked it - nothing seems to work. What should I do. I do have the scum ball - zorbie products also. I have only had the hot tub since the 2nd week of June. I have cleaned the cartridge (put in a new one actually)
It sounds like lotions, cosmetics, or sun tan oils may be causing your problem.
Especially in summer, people are jumping in and out of pools and spas and don't think to shower off (especially their sun tan lotion) before getting in the tub. Because these lotions are oil based, they float up onto the surface of the water and typically create a scum line much like what you have described (some people say it can sometimes look like peanut butter - yuck). Be prepared, it can sometimes take days to clear this stuff out of the water.
I would suggest purchasing a natural enzyme product to help break down the oils and lotions. You typically only have to add these weekly or when you have problems. A Scum Bug or Scum Ball should help as well - just keep these in the hot tub when you are not in it. Also, the best oil pads are the ones with a lot of surface area. The oil catches onto these and they are easy to rinse. Keep your hot tub filters clean by soaking them in Filter Cleaner when these problems arise. It is best to have two sets of filters on hand so you don't have any down time while you are cleaning one set.
But, the best way to prevent this problem entirely is to make people take a shower before they get in. Even if they are clean people - the cosmetics and oils from lotions wash off in the tub. It may be hard to ask them to do so, but it sounds like you already know the alternative.
By the way - Clarifiers are made to coagulate small particles so the filter can catch them. This is why you will see foaming right after you use it.
Please let me know if this helps.