I think your stocking list needs some work. Depending on how large the fish are, they could easily be contributing to the problem. I would start removing them according to what the problems are:
2 angels- OK if they are M + F, or 2 x F, but 2 x M can cause problems.
2 buenos aires tetras-I suspect these nip plants. Schooling fish.
2 bala sharks-These fish reach a foot long, live in schools, and eat plants. They startle easily, and can kill themselves crashing into the end of the tank. A 6' long tank is barely enough room. 8' is better, with a cushion of plants at each end.
1 long Fin rosy barb- Cool water fish, not compatible with the warm water that Angels need. Schooling.
5 black skirt tetras- Schooling, and 5 isn'r really enough. IMO look a lot like Angels, and I would prefer something else, but that is just me.
7 red skirt minor tetras-Nice. Schooling.
1 albino Cory-Cories are social fish, but many are OK with other species. Some prefer to hang out with similar looking fish.
1 emerald Cory
1 peppered Cory
1 clown loach- Social fish that can reach a foot long. Really need a tank double this size. Prefer lots of water movement (they come from rivers). Some Clown Loaches seem to like punching holes in large leaves.
1 eclipse catfish- http://www.planetcatfish.com/common/...species_id=159 Gets WAY too big, and is a carnivore. Will eat all the others as soon as they fit in his mouth.
1 pictus catfish - Nice. Got plenty of cruising space? Active guys!
1 kuhli loach- Social fish. Should fit in with the others, but need more of them.
1 peacock eel- Gets pretty long, I think I would be planning a larger tank. Might be OK in this tank, but barely. May eat smaller tank mates.
2 plecos - What species? Commons? They get between 1'-2' (depending on species, several are sold as Commons) and have a tendency of eating the slime coat off slow moving flat sided tank mates, like Angels. If you want algae eaters then a single bristlenose would work in this size tank.
I would trim the mid tank schooling fish down to one species, and get a dozen or more so there is a proper school.
Get more Cories. More Kuhlie Loaches.
Get rid of the larger growing fish (Bala Sharks, Eclipse Cat, Plecos, Clown Loach, and maybe the Peacock Eel).
OR plan a larger tank to include the Eel, Clown Loaches (they are best in groups) and perhaps the Pictus, then add some appropriate (larger) schooling fish.
2 mated Angels
12 Phantoms or other schooling fish, too large to fit in Angels' mouths, but small enough that a dozen does not over load the tank.
6-12 Cories OR 12 Kuhlie Loaches
1 Bristle Nose pleco