Classic 2000 hob

Are you running activated carbon? Have you used any chemicals to treat something in the tank? Dechlorinator? Algae remover? Red slime?

Well, the dechlorinator is causing the issue. It acts in the same way if you added soap to the water. It will make the water be able to intake more air and cause the micro bubbles. You will need to remove the dechlorinator from the system in order for the skimmer to go back to normal.

If you are using RO water, then you dont need dechlorinator. RO removes chlorine from the water.

There are several common reasons a protein skimmer will overflow but the most common is a chemical within the water itself.

Chemical Reaction - Some chemicals react with the air that the skimmer produces and causes the skimmer to over produce foamate. Chemicals known to cause skimmers to overflow are, red slime remover, medications, reef/frag putties (epoxy Putty) frag glues, water conditioners, dechlorinators, stress coat, NEW filter socks, newly mixed salt, bacteria (seeding) additives as well as other dosing medias. In order to remove these chemicals from the water column we suggest that you do several 20% water changes over the period of a month and add a good amount of fresh activated carbon to the system and change out every week till the skimmer has returned to normal operation.

You should not use normal tap water for salt water tanks. You will end up with a real bad case of algae. Salt water is different than Fresh Water. For salt water, you should only be using RODI water. You can either purchase it at your local store or what most people do is purchase an RODI unit so they can make their own water anytime they want.