There are many reasons that bubbles escape from a protein skimmer and can vary depending on the model and the situation it is in.

• The aquarium has only recently been set up or a large volume of newly mixed seawater has been added. If the aquarium is new there will be limited to no organic substances to react with the bubbles inside the skimmer. this can result in bubbles being washed out of the unit and is normal. This will usually correct itself as the aquarium matures.
• The skimmer may be newly added. When protein skimmers are new the charge of the plastics that the unit is made from will effect the way the bubbles behave. This can result in bubbles escaping from the unit or the excess production of clear skimmate. This will settle as biofilms form on the surface of the plastics and the skimmer 'beds in'.
• Additives, foods and supplimets can be surfactants. Many of the products added to an aquarium will be a surface acting agent and can cause changes in surface tension. It is quite common to see the foam level drop in a protein skimmer due to a food being added to an aquarium. As the surface tension changes the size of the bubbles inside the skimmer can change or the bubbles can be direcly affected. Usually the skimmer will return to normal after a short time, if there is a persistant problem it may be worth determining what food, additive, or supliment is causing the issue and seeking an alternative.
• The venturi is becoming blocked. As the air flow in to the venturi becomes restricted the volume of water to air increases inside the unit. This will cause the water throughput to increase washing bubbles out or the skimmer exit. In most cases the skimmer looks to have the normal amount of air inside it but over time a ring of salt or calcium deposits slowly restricts the movement of air, once cleared a difference is usually visable. When clearing the venturi it is always best to check that the flexible tube and any taps are clear and unobstructed.
• The outlet adjuster needs cleaning. Most of the Deltec protein skimmers have a fine water level adjuster. This is often located in an upright tube where water exits the unit. Bacterial mulm or debris can sometimes build up here restricting the outlet, in some cases causing a syphon effect dragging bubbles out of the body. The adjuster can be removed by using your thumbs to push the cap off of the top of the outlet pipe that holds the adjuster rod in place. It should then be possible to slide the assembly out of the tube for cleaning. The tube itself and the adjuster should both be cleaned. When removing or replacing the adjuster assembly do not use the dial on the top of the rod to pull it out or push it back in as it may become damaged.
• The pump needs to be cleaned. To keep the skimmer performing as it should the pump will need to be periodicaly removed from the unit, stripped down and cleaned. Care should be taken to ensure that the impeller is free of calcium deposits that may restrict its movements. When re-assembling the pump make sure all components are replaced correctly, if in doubt consult the products instruction manual. In most cases removing the pump for maintenance envolves dismanteling the skimmer, it is always a good idea at this point to clean all components before re-assembling the unit.
• The skimmer is set up incorrectly. Makes sure that the settings on the pump, if adjustable, are appropriate and that the protein skimmer is in the correct water depth. Consult the products instruction manual to confirm the set up is correct.
• The protein skimmer is positioned in a area of high water flow. If there is an oulet of a pump blowing across the outlet of the skimmer or the water flow past the outlet is strong water can be drawn out of the unit resulting in bubbles being drawn out. Re-position the skimmer so that the outlet is shelted from strong direct flow.