For all those using protein skimmers: There is a water quality/condition called "surface tension". This has everything to do with protein skimmers foaming or not foaming, no matter the make or brand of protein skimmer, it is a water quality/condition and not a protein skimmer issue.
What this means is that anything added to the aquarium/sump water will have an affect on the foaming of the skimmer, or lack of foaming. Anything added to the water will change the waters surface tension, and the foaming conditions.
Ever notice your protein skimmer stop foaming when you stick your hand/fingers in the water? This is due to skin oils changing the surface tension, and the reduction of foam.
Not all protein skimmer companies make note of this in their instructions (and very few even know about surface tension) leaving the hobbyist to believe their protein skimmer is at fault, which certainly is not the case.
I always advise hobbyists to observe their protein skimmer before adding anything to the water, add the product, then watch what the protein skimmer does. This way you will know what can cause the skimmer to stop foaming, or foam profusely and then know what to expect or to do to avoid water spillage.
Some products such as epoxies, Amquel, Novaqua, StressCoat, and some foods can cause protein skimmers to foam like crazy, and require them to be shut off until they don't overfoam anymore. Other products can cause a reduction of foam such as those fake rubber silicone corals, foods, chemicals, etc.
Bottom line: it is the customers responsibility to observe and to know what products do to the skimmers foaming characteristics.
Jeff
Lifereef Filter Systems
