Well there definately not eggs.
I am curious to know if you use a water softener on the water that you put in the tank...maybe it is salt from the softener that is collecting somewhere in the tank (maybe on or near an airstone, like salt creep) and finally floating to the top.
This seems like this is possible, I do use chems on my water, and the house has soft water...but still wouldnt explain it only happening in 1 tank. Ive searched everywere I can think of that it could build up, and cleaned everything that could hold it.
Since it doesnt seem to be hurting any of the fish now, im gonna wait till I find another one floating in the tank and get a pic of it.
As for them getting along it took along time to pick the right fish from my other tanks for it to work.
Apreciate all the help, and any that comes between now and the pics.