While a picture is worth a thousand words, a bit more info would help us help you.
For example, new spa? New fill? Test results?
As you noted in this thread, this is a fairly new spa. If you did not do a thorough decontamination procedure when you got the spa, then you should do so. This either means an intense superchlorination (100 ppm for an hour or two) and/or use of Spa System Flush (or possibly Swirl Away). New spas are tested with water in them, but when they are drained the pipes and other areas are not blown out so water remaining in them for weeks or months has biofilm form. Also, new spas have leftover chemicals (sealants, etc.) in them that need to be removed.
You say (in the other thread) that you are using SpaFrog and bromine, but what are you using as a primary oxidizer? Bromine is a decent sanitizer, but not a great oxidizer so most people have a bromine feeder set to a low level for a baseline sanitation if the tub were not in use and that after each soak they add either non-chlorine shock (MPS) or chlorine as the primary oxidizer to get rid of bather waste and to activate more bromine. Your ozonator should also be getting rid of bather waste somewhat so I suspect that it might not be working properly.
16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"
Sorry about so few details. Fairly new to this, so I don't know what's important. The spa is fairly new, installed in October. The water in the photo is only a week old. I'm using HASA hi-temp spa oxidizer ( potassium monopersulfate). Frustrated as ****!
Step I would take to get rid of the slime and to be sure it doesn't recur.
Add 1/2 gal unscented bleach. Run all pumps on High and uncovered for and hour.
Dump the water.
Rinse of the filter and soak in a tub with another half gallon of bleach for a couple hours. Agitate it every 1/2 hour.
Scrub the tub and rinse. Refill.
Put filter back in
Repeat all of the above.
Balance water. Check it regularly.
Going forward, use either bleach or lithium hypochlorite weekly, at a minimum. Heavier usage will require more frequent additions.
If you are using bromine tabs, put three of them in a floater weekly and don't forget.
Even it there there are no visible issues, change the water regularly. With light residential use (2 people, 1 hour/day), I like to see it changed at least every 3 months. More usage, more frequent changes (4 people twice a day = every two weeks)
Soak the filters overnight in TSP at water changes.
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