I have a 4" long crack in the top of my 180g. acrylic tank. the crack starts at the corner overflow and ends about an inch from the side of the tank. Seeing as how the top braces the tank, is there a good way to fix it, or is the tank now junk?
One of my tanks have three of these cracks on the top.
1, use a drill to drill a small hose at the end of the crack to stop it from progressing.
2, use WeldOn to cement the crack back if you can clean the edge really well (RO/DI, completely dried, etc.) Use clamp to hold the tank in shape (may need to drain some water out) if you can't apply the pressure for 24 hours non-stop (hint: get a pillow so you don't have to scream to your wife for it when it is bed time...)
3, use a piece of scrap acrylic (similar thickness) to patch over the crack if you are paranoid.
I got mine from a local glass company. They had to order it for me, but it was cheaper than ordering online, then paying shipping charges. I ended up just cutting the cracked piece out with my Roto-Zip, cooled with water to keep it from melting. I then used this piece as a pattern to cut out a new piece. I then glued it in place, left it alone a couple of days, then sanded and polished it out. Turned out pretty well I thought. You don't really see it anyway, because it's on the top.