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Agreed, a larger tank for your angel and shark (angelfish would be fine if he wasn't becoming aggressive, I don't have experience with sharks and believe they absolutely need more horizontal room)
For immediate temporary help, do you have plants and/or decor to break up the tank, create territory for your angel and hideouts for the tetras? I would add at least 3 more neons, preferably get it up to a group of ten. They are not heavy on the bioload, feel and act much safer in a big group.
GiVe Me sHrEd TiLL i'M dEaD
-Kat