Hi again. I'm sorry if I sounded harsh. I do just want what's best for your fish. You didn't seem to accept that the fish you have aren't suitable for your tank or as tankmates for each other and that's why I felt a little abruptness was necessary. Please understand that I didn't just come up with what I said to make you feel bad and I'm sorry it was not subtle or what you wanted to hear.
I also don't know EVERYTHING there is to know about fish. I love this hobby precisely because it is impossible to ever learn everything there is to know and you can learn something new all the time if you take the time to listen. However, I do know some things and I have given you what I beleive is sound advice. Whether you choose to take it or not is entirely up to you and there is absolutely nothing I can do about it. But please realise that I have researched the fish you have and others and taken the time to tell you that your fish do not work together or in that particular tank. I have done this because I care about their lives and want you to take good care of them. It was never meant to make you angry or upset.
Now about those tetras - I did not say they deffinately damaged your angel - I said they very well might have done and that the cause of your angel's troubles could be a secondary infection. I did say black widows/skirts are known nippers and they should not be kept with long-finned, slow moving fish. Angels qualify as long-finned and slow moving.
As for the shark being freshwater and fitting in a 30 gallon - that simply won't work. And the plec simply won't do in a 30 gallon permanently either. I don't know whether you think this because someone told you otherwise or you just like the fish and want to keep them so much (as they are admitedly both wonderful species) but, regardless, you need to do what's best for the fish as a responsible fish-keeper (which I believe you are as you seem to want to know what's wrong and correct it).
Maybe that means getting a couple new, big tanks or maybe that means re-homing some of your fish. Whatever you decide, good luck to you,
and sorry again if you misunderstood the purpose of my previous post.