White poop can be a normal thing, or it can mean internal parasites. It really depends on how it looks and what you're feeding. Here's what I mean:
If you're feeding mysis and the fish has solid, long poop that breaks off quick and clean, it's probably fine. If it's hanging from the fish for a prolong period of time, and it looks like the fish is shaking trying to get it off, it's probably parasites.
If you're feeding New Life Spectrum pellets, or any kind of hard, high protein food and you're getting white poop it could be 2 things. 1, the fish could be getting used to the food and is a little constipated from the high protein. 2, the fish has internal parasites.
White poop does not equal parasites all the time, it really needs to be looked at with what your feeding and how long. If it is real stringy and hanging for a long time it most likely is, but like I said you need to think about what the fish has been eating and how it's acting.