You really should have more filter capacity. I don't think that you're overstocked, but a healthy amount of water movement not only help to keep the tank, but provides uniform oxygen for the fish, but for the bacterial filtration as well. Your ideal filter should turn you tank water over 3 times an hour. My 55 gallon tank runs at 150 gallons an hour. Don't go by a manufacturer's up to size, go by the gph of the filter. If it's cheaper for you, check the gph on your current filter. If it says it pumps at 30 gph, then you can just add a second filter that runs 60 gph. But if they're hang on back filters, you need to make room for it, you'll need an outlet for it and there will be extra filter cartridges to buy. So in the long run, it would be butter to get a single that pumps 90 to 100 gallons per hour. If you do get a single pump, I would still try them both able to run together for the 1st month or try to find your same brand that holds 2 of the same size cartridges as your current filter. That way you will already have one cartridge that already has beneficial bacteria. If you just completely change to a brand new filter instantly, you will suddenly have an uncycled tank...very dangerous.
Good idea. The Aquaclear 50 would be the right size for the tank and sell for about $38.00.Yes the C3 should be fine, but I have to say that I had problems with the impellers of both my C4, to the point where I decided recently to get a canister filter. If you google it you will see that a lot of people had similar problems.
I would look at getting an aquaclear instead.