i came across this idea today when i was trying to sort out some of the fungussy eggs from the healthy ones. this is a very reliable method i found.
what you need to do is VERY gently take off the eggs from the plants and put them into a tub. only do this a few days after the spawning has taken place as they will be less well 'glued' to the plants.
after you have collected all the eggs, get a straw and suck some eggs up very carefully so you dont suck too hard and end up having caviar for tea! put your thumb or tounge over the end you sucked from. put the straw to the light the first time you do this and you will be able to see the healthy eggs sinking quite quickly to the bottom of the straw and the unhealthy ones sinking very slowly.
now put the end of the straw in the water so the healthy eggs can sink down into the water. hold the straw up to the light again to make sure there aren't any you missed and then you can take your tongue or thumb off the end of the straw into another tub and dispose of the unhealthy eggs.
et viola! no fungus scares any more!