Protein skimmers are arguably the most effective filtration devices for saltwater aquariums. Unfortunately, these normally reliable workhorses can be brought to their knees with just a couple of small, inconveniently placed pieces of debris. A grain of sand, particle of activated carbon, or wayward snail can get lodged in the needle wheel impeller of a protein skimmer and essentially halt all skimmate production. Additionally, small salt crystals can accumulate in the tubing of the skimmer’s air intake and severely restrict air flow and bubble production. And if these were bad enough, the impeller shaft that holds the needlewheel impeller in place can also break easily (if it’s ceramic), which will basically render your skimmer completely useless. So, check your protein skimmers and perform necessary maintenance on them regularly.