how big is the tank ?
Odinium is like a very very fine grey dust on the skin. If developed you might see small dust particles on the pectorial fins or any fin really, – you might see the fish wawe those pectoral fins (not sure about the english name to them, but those on the side :)) more than usual.
Yeah, caching paros can be a nightmare, which is probably why I wouldnt keep them in a bigger tank with other fish 🙂
But, – if I have to catch any paro, what I would do, – if serious – I would slowly rid the whole tank of everything. Just take it up slowly (look for any paro trying to stick to the wood or something.) But if you do it slowly, over one day say, – and leave the tank to settle, so you can see.
Then you can spot the paros, and target them more easily :). If you can get them up to the front glass, its easier to get the net over them, holding the net up against the glass. I know they dart around like … – but normally they do not get hurt.
Once you have a fish in the net (up against the front glass) you can use a little tortlamp to get the paro to move to the back of the net. They dont seem to like the light so they seek inwards).
Thats pretty easy :S