I believe it was the o ring on mine. Now I have heard great things about the 305 and 405 from a few users, but the 304 was the one I heard the worst about, but it came with it, so I used it. I would have it in the bucket for awhile just in case
Just search fluval 304 leaking in google and you will find lots.
Mine was also terrible to prime compared to my other fluvals and other canisters. So I am pretty sure I got a defective one since like I said before, my fluval 204 was fine, no leaks and easy priming. As for care, I only had them a few months and both of those fluvals came from the same person so I am assuming he treated them the same way haha
Just search fluval 304 leaking in google and you will find lots.
Mine was also terrible to prime compared to my other fluvals and other canisters. So I am pretty sure I got a defective one since like I said before, my fluval 204 was fine, no leaks and easy priming. As for care, I only had them a few months and both of those fluvals came from the same person so I am assuming he treated them the same way haha

