I am about to buy a 240 and set it up as a species tank. I have found a great deal of information, but not much dealing with water flow. How much is too much and how little is not enough? Does it matter?
I have read 6-10 cycles a hour our ideal, however with that large of tank you could probly get away with much less since it would take a very long time to build up waste, however, someone please back me up because I have never delt with tanks so large.
I set my tank up with about 20x per hour turn over. It all depends on how you direct the flow, you don't want it to be like a river in there. I think having a lot of flow through your wet/dry and your skimmer are good because that's what gives so much oxygen to the water.
If you have too much water through a skimmer it can just pump water into your collection reservoir, make sure it's all waste thats coming through or you will have to do more water changes than necessary
I'm going to buy a skimmer from Andy at Myreef Creations. These skimmers require a high flow pump. However, the tank will be drilled and the equipment will be in the sump. The overflows will be enclosed to prevent escape.
I am not a fan of wet/dry filters. They tend to be nitrate factories. That may not be as huge of an issue with an octopus as it is in a reef, but it is an issue none the less. I prefer to use live sand/live rock and water changes to take care of the biological filtration.
If the octopus can withstand higher flow, I will probaly set up a surge device for the majority of the flow and use a smaller return pump.