I found that using netting to cover the overflow box can be quite an annoyance!!! It quickly becomes clogged and interferes with water flow plus it is a real pain to clean. I have hit upon another solution. I am goig to cover the top of the overflow box with acrylic with a hole cut out for the siphon tube. Thus, the water can still flow through the slots but a curious octo cannot enter the box and end up in the sump. (Hopefully) I'll post some pics of this solution if anyone is interested.
i am getting ready to do this to my hang on overflow box as well. i have some extra plexiglass at work.
but after looking at it again. i havent put water in this tank yet it appears if i put it in the highest position the glass top my sit nicely on top of it. any way i figure ive got at least 3 months to work it out. although i think i'm gonna oder a baby bimac in 2 months to go in a new 15 tall i recently set up untill the 37+10 is ready in another 2 months.
another thing..about the u tube. consider installing a air valve in the top of it so you would'nt have to remove it to get a siphon going. just attach air hose open valve and suck. hold your thumb over the hose and shut the valve.
this would probably allow a tighter fitting u tube!!!
In my opinion, covering the overflow box is an invitation for disaster. If the octopus can park itself in the U tube, then U have yourself a big problem as the sump keeps pumping water into the tank.
regular fiberglas window screening and a rubberband is usually suitable for any intake grille, but it will need to be brushed out periodically.
Plastic needlepoint grids sold at any arts & crafts store is a ceph keeper's best friend. A huge sheet costs a buck, and regular scissors can cut it. There are a million ways to fasten it to things, but I've yet to discover anything better than a dab of silicone.
Of course, if you just keep a bimac, there is no need to cover or screen anything.
One of the greatest things about studying behavior is it's diversity. Sure, terrible water quality could motivate an octopus to leave it's aquarium, but that's as much a guess as anything. Who's to say those two octos didn't kamikaze because something in the same room as the aquarium looked neat enough to warrant exploration? Perhaps the sound of a pump drove them crazy. Maybe it wanted another bite of iguana tail. Who knows?
By and large, I've found that bimacs stay put. When I visted the NRCC, their bimac tank was a large tub with no lid. When Forsythe took me over to the now defunct CephSource warehouse, I saw dozens of bimacs in equally lidless aquaria. I've lost count of how many bimacs I've kept, but only one ever wound up on the floor, and he was well into senescence.
The best advice is to get to know your octopus. In the beginning it's probably wisest to take precautions, and then, if you deem it reasonable, remove security measures to make your life easier (anything that you screen with any octopus-proof mesh IS going to clog sooner or later)
Of the two instances of bimac escape that I know of, both went out the top, not over the overflow.
A really interesting aspect is that in both cases, the escape happened shortly after the bimac went on a little trip - to a school in each case. Did seeing the larger world motivate them to climb out? In the later case, there was another tank nearby, so that could have also helped.
One thing I have noticed in keeping Ollie is rapid change of interests and behavior. There was a time when she would have climbed out in a minute! We let her do a supervised "sit on the edge of the tank and feel around", and that seemed to satisfy her. It was more like coming out to visit us. Now, with the eggs, I don't think she has any interest at all in leaving.
I Think escape is very much a species thing! Our midgets rarely escape (once that I know of) but our P. cordiformis can be a regular Houdini! So we have EVERYTHING covered! Drains have caps, the tank is sealed to the ceiling. Only problem we have now is if one of the staff leaves the "door" ajar!
It's also an individual thing (even with P. cordiformis) we've had some that we've spent many hours retrieving from all over (including halfway up the stairs to the staff room ) but others (like our current one, Mrs Henry) don't seem to be interested in even trying!