A lot of the stuff around the toads is protein left over from the eggs and is a normal food for the baby toads but the other stuff is likely to be a product of debris breakdown or excess slime coat sluffed off as it gets old. I don't know why it would appear as a layer in the winter unless there just isn't enough circulation. Do you run the filter since you aren't likely to get ice cover?

yes the pump runs 24 hours a day, 365 days a year. i use a homemade prefilter that is a good bit larger than the one that came with the pump as it clogged way too easy. i have a pressurized filter with the bio- balls in it. the water itself is clear as gin. just that gookie stuff on the bottom and some string algae on the water falls, which doesn't really bother me much. the sides have a nice layer of algae on them also, but from my reading that is a good thing. my plants will eventually become clogged with the muck too. i have added 2 small bales of barley that is advertised as being sufficent for 1000 gals which is about what my pond is. i can't vaccum now because the toads have hatched and there must be thousands of them everwhere.

One product of rotting barley straw is hydrogen peroxide. That is the only beneficial product in the pond and the amount produced is irregular to say the least. You might be better off just buying a bottle of H2O2. It would be cheaper and less likely to cause problems. All of the studies I have seen say that the much touted affects of barley straw are unproven. The only thing it might do is reduce string algae and the bottled H2O2 does that better.