My fish tanks crazy odor?

When you change the water, you shouldn't be replacing 100% of the water each time - you are throwing off the balance by doing this. since you have a bio-wheel and a carbon filter they should be doing a good job. 3 gallons isn't a whole lot of water -the slightest thing that goes off-kilter will throw the whole system off. Let the filter do it's job - just add more water as water is needed, and resist the temptation to empty it completely - i bet it settles down before long. Also DON'T use any chemicals in the water that kill algae, etc. - those always cause more harm than good. AquaSafe is fine if it's just an ammonia/chlorine remover. Don't overfeed your fish either - that can foul the water faster than anything. One fish only needs a few granules of food, and if there's any left floating around in the tank after a few minutes, then this is probably where your problem lies. Good luck.