I run a two pools and a hot tub at a fitness center. The spa had foam issues about 4 years ago so we turned off the air blowers and now just run water jets. Since the air blowers were turned off, foaming has not been an issue until about 3 weeks ago it suddenly started foaming badly and I am at my wits end trying to figure out why. The spa is chlorinated with calcium hypochlrite and is drained once per week and shocked once per week. The foaming returns immediately after the spa is re-filled so draining it more often doesn't seem like it would fix it. Here is what I have tried so far:
1st, I tested the source water's calcium hardness and found it was only 80ppm so I've been adding calcium hypochloride to bring the hardness up to ~200ppm immediatly after the spa is re-filled. This seems to marginally reduce the foaming for a few hours after the spa is re-filled.
2nd, I've disinfectd and scrubbed the entire spa to try to remove any contaminants.
3rd I also soaked the sand filter with a filter cleaning product to remove an contaminants from the filter.