what size tank have you got the tetras in?
vinegar eels are a type of worm that you can feed to you fish that live in unpasteurized vinegar. they are very small, and you could either feed tose to your fish, or microworms that eat yeast

of course you could just feed them crushed up flakes if they are that small and only feed the worms as a treat

Kissys right that the tetra's colour should be more defined
Colour is controled by the neuroendocrine system (sp?), so loss of neurological control (e.g: due to flukes) can lead to colour changes in the skin.