Hi
I bought the 8 oz jar of ProGold (its like a measuring cup and a half approx). I think it's a good size to try out, I don't remember the cost but it would probably last you long enough to get a sense if your fish like before you buy the big size.
My fish seem to really like it.
The pellet size is pretty small I don't think your fish will have a problem with it.
Good luck with your fishes!