When we turn on our jets, sometimes the foam build up in incredible. What causes that and how do we control it? Thanks.

I've noticed that symptom when the cyanuric acid is high in my own tub. For me it seems to only happen (like you said) when the jets are on, and seems to subside and go away soon after the jets are off. I have solved the cyanuric acid problem by changing the water completely. Now my water does not foam and the cyanuric acid level is good. Coincidence? I think so.
Maybe try a water change? I change mine every 6 months and now have no problems with chem.

That foam most likely comes from the soap in your swim suits, as well as oil and sweat from your bodies. You will need to clean your spa and filter and refill; and make sure your swimsuits are rinsed properly, or only rinse without washing with soap.

If you cleaned your filter with cartridge cleaner rinse it properly many times, and run your spa with it in place to get all the foam out. Do that before you drain your spa.

Just wondering if this solved your foam problem. I 100% agree with the swimsuits and washing machine detergent. A minute amount can and will foam! I learned.

But,,,, I hardly ever use my spa anymore (D1 Sarena Bay) but do change the water every 2 months approx. Even though I keep it balanced, I'll get increasing amounts of foam over time. I use "foam reducer" that you can buy at the pool store and that works but I sure would like to know why the foaming starts anyway if no one is using the spa. Something... chemically must be going on. (yep filters are cleaned/replaced often)