Having a tank with saltwater and a filter with a biowheel is a complete receipe for disaster in a marine aquarium. You need live rock and live sand won't hurt things either. These things can't 'break' and do a much better job of filtration than anything else. Also, you need a protein skimmer. These things are absolutely neccessary. If you are going to keep a tank and put delicate sea life in it, get everything you need and don't skimp or you will have a crash sooner or later.
Better luck to you in the future, but it sounds like this needs to go back to the drawing board. If you caught an octopus once, you can catch one again!
Oooo... Kinda too late for that cuz I put on an extra filter and fixed everthing on the old one cept for the bio wheel. But I know what wrong with it. It won work unless it below the highest waterline on the tank. Kinda stupid dont u think? Oh well.... I caught a new octo too! Ooops I didnt know I had to let my tank startover. Hes smaller than the last one and I call him cephie as well. Hes a cute lil bugger. He inked the tank a lil too. :P O well I guess we will see how he does.