I'd say the tubes of 100% silicone at home depot would do it but it won't truly adhere to acrylic. If it not a load bearing baffle it'll work to at least keep it in place. Weld-on is really your best bet though. If you go the silicone route, make sure it doesn't say algae resistant and 100% silicone. You don't want that algaecide stuff in your tank. Ace (Hobogato) may be able to repair it for you at a very reasonable price as well...