Hot Tub Main Filter clogged with hard white/tan scum

[Snowshoe]

This has only happened a few times over the last 15 years. When I pull my filter for cleaning, I clean my filters every month, the main filter is plugged with hard tan scum. In the spa itself there is some, not a lot, of what looks like strings of white jelly floating. The water is crystal clear and the CL level was a little low but not bad.  See attached photo of main filter and aux filter. The aux filter is fine. Does anyone have any ideas on why this happens?Plugged Tub Filter.pdf

[RDspaguy]

Your attachment didn't work.

This is a buildup of bacteria feeding on accumulated contaminants in your spas pipes called biofilm. Use a spa flush product, drain and refill. Watch your sanitizer and ph. Sanitizers are only effective within a certain ph range, so if your ph is way off, your sanitizer does not work.

[Snowshoe]

Thanks for the response I will check my attachment and my ph level