Safe to use Super Glue?

Super glue would most likely be very toxic to fish. Just use silicone to fix the piece. I use the DAP brand found at Home Depot or other hardware stores for a couple of bucks.

actually supper glue should be safe to use. people with saltwater aquariums use it all the time for mounting corals to rocks, and i have used it to attach plants to driftwood. if you are still a little concerned just let it dry before you put it in the aquarium.

I wouldn't risk it, get some window and door silicone from GE at Home Depot, works wonders on everything, and it is very likely that you will use it over and over.
Jack

As long as that superglue is a cynoacrylate it would be fine in your fish tank, just let it completely dry. As mentioned above many reefers use it in their fish tanks for attaching corals and what not, I've also used it in my fw tank for attaching some plastic parts to the powerhead with absolutely no side effects.

The saltwater guys have been using cyanoacrylate (super glue type) for years to attach corals. I'm using some now to build my underwater decorations because it's fast and not toxic when cured. Then I follow up with an epoxy.
If you need strength to hold two large pieces together I would use an epoxy instead of cyano.

Silicone will shrink over time. I had this happen to me late last year when a decoration I built began to fall apart underwater after a about three months. It was aquarium grade silicone.