Foaming can happen for many reasons, so let's talk through them.
There are different kinds of foam that can be created in a spa or hot tub. If we were to break these down into three categories, they would be:
- contamination,
- a chemical conflict
- enzymes and surfactants.
Contamination foaming
Over time, dead skin cells and other non-living organics that have been oxidized build up to a point where the water becomes fouled. Not only will the spa water be discolored and ugly, it is likely to have a concentration of oily film on the water's surface and perimeter of the spa. Spas with this type of aged water tend to foam each time you add sanitizers or oxidizers to the water. So in general, heavy use puts a lot of non-living organics in the water, and eventually they can lead to foam.
Other organics like tree droppings (particularly holly tree berries) tend to foam up when oxidized too.
Chemical conflicts
Another common foaming is when certain chemicals conflict with each other. We have seen this happen especially when spas/hot tubs have ozone or AOP systems. These secondary oxidizers are powerful, and they attack just about everything...which is a great thing for water quality. But if your water contains chemicals that conflict with such systems, foaming is a likely outcome.
An example of this would be polyquat algaecides and ozone. Another could be alternative sanitizers like biguanides and chlorine. Or biguanides and enzymes. Or polyquats and enzymes. The list goes on and on.
The point is, be aware of the chemicals you are putting into your spa, because especially in small water vessels, chemicals can be overdosed easily.
Enzymes and surfactants
Enzyme products like CV-600/700 initially foam any water when adding the purge dose, because they contain a natural surfactant in them. A surfactant is something that repels lipids and keeps things separated in water (think dish soap in greasy water when cleaning dishes). Proper use of our enzymes has an initial bubbling from the surfactant, then hours later, clusters of small bubbles of carbon dioxide off-gassing.
If the water is turbulent and warm enough (like a hot tub usually is) enzyme products are likely to foam temporarily. Thankfully, this foaming is harmless, and is just a byproduct of what enzymes do.
Foaming is why we created CE-SPA, our chitosan clarifier with enzymes that was designed specifically for spas to be less foaming. If you are still having foaming issues using CE-SPA, just give the spa some time with the lid propped open so the CO2 can off-gas, and the foaming will go away in a matter of hours. If not, think about other chemicals that could be in the water potentially conflicting.
Enzymes can foam when interacting with complex organics like antifreeze products, polyquat algaecides, and certain products we put on our bodies. Just be aware the foaming is part of the process, and it's evidence the enzymes are doing their job. So vent the lid to your hottub and let the CO2 off-gas so the enzymes can complete their work.
Conclusion
Foaming can happen for a number of reasons. Heavily-used water eventually gets saturated with non-living organics and who knows what else. Oxidizers like chlorine, bromine and ozone can create foaming when attacking these substances. Chemicals can also conflict, leading to more serious foaming. Finally, enzymes naturally create some foam as a byproduct of them doing their job (breaking down carbon-chain non-living organics into CO2 and off-gassing).