Recently, Ive started using some sponge filters, After ordering I realized I did not have any check valves so the only thing near me was Pet Smart and has hate to have done it I bought a Top Fin check valve. After getting it home you could not even blow thru it. I also went to a LFS in a near by town and they had some for $1 each no name brand so I bought 3 of them. Well 2 out of 3 worked. I recently pordered one from a mail order store. It was $2 so I thought it may work it also did not. Anyway I hate buying things that don't work. Any suggestions on a brand of check valve that works. thanks