I would change the water a little more often. I agree with Shawnie that stocking might be causing stress.
I plugged i your tank parameters here, without including everythin g in your tank:
http://aqadvisor.com/AqAdvisor.php?A...&AqVolUnit=gUS
and got this result:
Warning: Angelfish will likely to fin nip Guppy.
Warning: At least 6 x Peppered Cory are recommended in a group.
Warning: At least 6 x Glass Catfish are recommended in a group.
Warning: At least 6 x Head and Tail Light Tetra are recommended in a group.
Warning: Angelfish is too big to co-exist with Head and Tail Light Tetra
Warning: Angelfish is too aggressive to co-exist with Head and Tail Light Tetra
Warning: At least 6 x Cardinal Tetra are recommended in a group.
Warning: Angelfish is too aggressive to co-exist with Cardinal Tetra
Warning: At least 6 x
neon tetra are recommended in a group.
Warning: Angelfish is too big to co-exist with Neon Tetra
Warning: Angelfish is too aggressive to co-exist with Neon Tetra
Warning: At least 6 x Cherry Barb are recommended in a group.
Warning: Angelfish is too aggressive to co-exist with Cherry Barb
Warning: At least 3 x Clown Loach are recommended in a group.
No errors.
Warning: You NEED to add more aquarium filtration capacity!!!
Your aquarium filtration capacity for above selected species is 31%.
Your aquarium is 157% stocked.
edit: oh, and a couple of yours weren't on the list do I substituted the best I could