I just wanted to drop some quick praise for the DC versions of the DOC skimmers. I have run a smorgasbord of AIO in tank skimmers, and have never found these smaller skimmers to be satisfactory. I was convinced that the only way to have a decent skimmer in a small package was with an airstone. I have run the original DOC skimmers, and they were good. But I didn't think regulating the skimmer via airline valve alone was effective enough. The DC version is a game changer. I've been running the 9004 DC version for a while now on my smaller reef, and it is simply fantastic. It is consistent, and I can skim dry or wet with a simple turn of a knob on the controller. Props to Tunze for continuous improvements on their products.