Part of the problem might have been that a lot of snails died and were decaying producing a much higher level of ammonia than your previous cycle could handle; though in truth 51 days seems like a long time. To the general question i run most of my aquariums on various size sponges; my 10 has 2 relatively small 2x2 sponges - one in each back corner and my 29 larger matten filters (just a giant sponge with a bit more water movement to force the water though the sponge). If you think about it long enough a canister filter is nothing more than a giant sponge filter with a strong pump to push a lot of water through mostly a lot of sponges
