I am thinking of dosing my tank with powerful antibiotics to try and get whatever parisites out of this tank.

I will probably lose some plants, which sucks, but I WANT A SCHOOL OF TETRAS DAMMIT.

Do the dieing fish look like they've been beat up by the other fish?

I'm thinking about getting a diatiom filter for my tank as well so any little parisites can get filtered out of the water.

My lfs said that my pH was too low, at 6.8. I thought 6.8 was perfect for tetras, but the store has them in pH 7.8, so he thought it may be pH shock even though I took hours slowely getting the fish acclimatised by slowly lowering the pH.

These are all the ideas I can think of that may help you.

Good Luck. PK

each fish that died has had ruffled fins and had a lot of mouth movement.