This is often an indication that you may have a skimmer that is too large for your size aquarium or you have no organic waste to be pulled from the water. Once the skimmer pulls out all the waste matter the skimmer sits in idle till the waste level builds back up to build a healthy foamate.
Make sure that the water level within the sump stays stable at all times. The use of baffles and or an auto top off will help maintain consistent sump water levels.
Another important thing to remember is that whenever you put your hands in the aquarium or feed your tank’s inhabitants you introduce oils into the water column which will break surface tension in the water causing the skimmer foamate to fall. It is very important that you clean your hands before working in the aquarium and remove any oils or soaps. Using fresh activated carbon helps keep down time to a minimal.
Adding chemicals can cause a reaction to your skimmers production of foam. It is best to shut your skimmer down while using any chemicals to treat algae or disease in the aquarium and follow up with large amounts of activated carbon to absorb the chemicals prior to starting the skimmer back up.