I "rinse" my food before. I don't know if that is the same thing as in presoak. get a net, drop the food in, run under COLD water. Then putit in the tank. You should do that will all frozen food.
HTH
Leopard
PS- It keeps your nitrates down
Just put it in a container, like a small butter dish or something, with some tank water for a couple minutes. I do this with my frozen food as well to thaw it.