
Welcome to FishLore
The forum seems rather quiet tonight. Like Elvis above, I don't know about Angelfish in particular however, there are potential problems with your tank that may cause the problem you're having.
Is it possible to have your water tested and post the readings for
ammonia,
nitrite and
nitrate?
Stress Zyme is a bacterial additive that claims to help cycle a tank. However, it doesn't contain the correct bacterias that process the ammonia and nitrates. I'd venture to say your tank isn't cycled and suggest you stop using it.
Keep a close eye on your water parameters, and do daily water changes when you start having ammonia readings and continue that until the tank is cycled. Your readings should be 0 ammonia, 0 nitrites with some (5-10) nitrates.
Your tank is over stocked.
Your pleco should be in at least 55g's. They get really big and produce much more waste than a 10g can handle.
Unfortunately Angels don't belong in a 10g either. It's recommended that one have at least 20 gallons and need a tall talk. Since they grow to be about 6" a peice, I wouldn't put 2 in a 20 gallon. Having them in too small a tank will cause their growth to stunt and deformities.
Your other fish are schooling fish and would do better with others of their own kind, but again 10g's isn't enough to add any more fish.
I'm sorry this post sounds so negative, I don't mean it to be but these are problems with your tank that you should be aware of.
Hopefully someone with more knowledge about Angels can more more specific about the discoloration you're seeing.
Best of luck!