there are no small skimmers commercially available (that work well) that I know of for a 12 gallon tank, however, There are several do it yourself versions, and Aqua C is slated to release a 'Nano-Remora' HOT skimmer in the near future, designed for nano's. I was going to build a homeade 'pico-remora' for my 1 gallon nano-tank, but when I changed jobs (same company, different desk/time) I had someone take care of it for me, found out he liked to shake his leg while sitting at my desk, this caused water to spill out, which he concientiously replaced with fresh water. I came in after being out for a week to a totally crashed system, whole rock of dead zoos, dead purple shroom, dead white and green striped shroom (i got from Sam), ded sawblade caulerpa (amazing) dead sexy shrimp, dead nassarius snails, and one hell of a trooper, a living dwarf zebra hermit (now residing in casa 'main tank' at home. needless to say, I haven't started it back up, that was slightly heart breaking.

Anyhow, water changes are crucial in nano/pico aquaria. skimmers help. you should check out www.nanoreef.com (I think that is it.)