oilen said:
I believe it is cracking because of the vibration caused by the piping it is connected to. It's piped into a recirc pump and into the ugj.
Ah, now we are getting somewhere! The vibration must be caused by the pump. If you don't address this problem, and just make the bulkhead stronger, it will be your tank that cracks next!
Is the pump connected to the bulkhead via hard pipe all the way? If so, use a flexible hose, eg a clear PVC hose like you can get at the hardware store, to make the connection. A flexible hose will not transmit the vibration to the bulkhead, and your problem is solved.
A regular plastic bulkhead should then be able to do the job just fine, but if you still want to use a brass bulk head, I have no objections. I don't think it will be toxic for the fish. But if you just replace the bulkhead and don't address the vibration problem, you have a disaster waiting to happen.