Hello Phonedave: Even after a successful plumbing purge using our Ahh-Some or the liquid and mixed Aqua Clarity maintenance product, it can foam a little if there are still remnants of the purge process that was not emptied out. Plus, as organics are released into the water as normal soaking continues you may periodically see small amounts of foam when the jets are on high. Ideally, after a 20-30 minute soak it is advantageous to wipe away any build-up you may see at the waterline and up to the top of the tub perimeter. If this is not something you do automatically the bio-goo will typically get caught in the filter(s) after enough circulation takes place. Wiping any waterline film will get you more mileage from your sanitizer. Foaming will also be mitigated over longer periods without draining. A good indicator to determine if you are approaching an upcoming purge requirement is to see how long the foaming remains on the water surface after the jets are shut off or turned down. Remember also that “off-gassing” takes place when the jets are first turned off. You will see the tiny bubbles rising to the surface. This is very normal. What I am referring to are foam with slight discoloration Inside the bubble. Glad to hear that you are using the Aqua Clarity. Please keep posting as to what you are noticing about the product. Your water clarity should be fantastic. Your filter(s) should be grabbing smaller and finer particulates with this product. The tremendous advantage of using Aqua Clarity is that you won’t need tp purge nearly as often since the “AC” is working 24/7 to prevent biofilms from attaching to surfaces. We keep most of it from sticking which means that your sanitizer reacts on it keeping your hot tub happy and healthy.