I'll probably just go ahead and try to re-seal the entire tank. Are acrylic tanks sealed similar to glass tanks where I would just use a razor to scrape away the seal and re-apply. I found this from another thread posted by brianp, "My understanding is also that silicone will not adhere strongly to acrylic. However, if the silicone is merely being deposited to serve as a barrier against leakage and does not have to bear any load or pull, you can use it to form such a simple barrier on acrylic (I have done this). The better method, is to go to TAP Plastic and acquire methylene chloride or other acrylic adhesive and one of those plastic bottles with the needle at the end. The needle is used to deposit the adhesive at the corner or seam, and it then moves between the two surfaces via capillarly action. The adhesive will melt and fuse the two acrylic surfaces. Be careful when applying...might want to practice first."