Hello once again: I have another question . I finally found a home for the two pirahna which occupied the 55 gal tank that I am setting up for the octo. My LFS took the on consignment. (I looked it up in webster's, apparently Consignment is Latin for "I'll sell them for $89.99 and tell you that they died".) Anyway, I have read much of the Octo's need for high Oxygen levels. Thus, I would like to know if I need to put an airstone in the tank or will the skimmer and sump return provide enough oxygenation??? Note that I am presently using a hang on skimmer until I build one for the sump. Full set up as follows: 55 gal tank with 50lbs live sand and 50 lbs live rock, hang on siphon prefilter, 20 gal sump with Magdrive 700 return pump (approx 450 gph at 4 ft) and a junky Seaclone skimmer. The sump and bio-tower are home made I have enclosed a picture. http://mysite.verizon.net/vze3zbpe/id5.html But I digress, so back to my original question, do I need additional oxygenation??? Thanks a bunch.