Used Saltwater Fishing Tackle

In a 29 gallon tank with heater & a 20-40 AquaTech filter, we have an assortment of very small to small non-aggressive, yet very active fish: 15 tetras ( 6 neons, 6 glowlights, 3 blue), danios 18 ( 3 striped, 3 spotted, 6 orange glofish, 6 lime/yellow glofish), 5 assorted male guppies with fan-like tails (had 6, but lost one a few days ago)... 38 fish total, all not more than about 1 inch long each, all are active & appear to be healthy. At present, we do NOT have live plants. What type of bottom-feeders &/or algae-eaters would be ideal for our current community? We'd prefer something that will stay on the small side & that is non-aggressive... we were considering maybe 3 small cory cats or a small plec, or a snail.
Also, water is clear & levels (pH, nitrates, etc) are ideal... is normal to have a fishy type smell?... it's not a strong smell, just faintly there when we open hood to feed. We've had the tank up & running for about 2 wks, but only a week with fish in it.