Do I need a filter or something?

Snails usually create tons of poop, at least in my case they always have. Have you tried sticking your vacuum right down in the gravel and allowing the gravel to toss in the tube for a few seconds? This will help remove any waste that has fallen deep into the crevices. Maybe you are over feeding your fish as well, try only feeding as much as your fish can consume in 2-3 minutes, and remove any uneaten food with a net. Fish do that all the time, if only they didn't poop all the time lol. An air pump will only help with water surface movement allowing for extra oxygen to be dissolved into the water. Try doing a couple smaller water changes twice a week. May I also suggest getting 2 more black skirts and at least 2 more phantoms, they should all be in schools of at least 6, but with the tank size groups of 4 should suffice.