Gweenie

I have a moor and a fantail. I used to feed them flake food, the advantage of this being that my nearsighted moor Freddy was able to find it and eat. I have recently upgraded to gel food- something I have wanted to do for awhile. But now my faster and much sharper sighted fantail Isabel is gobbling like crazy before Fred gets a chance. I am afraid to just put in more food, for fear Isabel will eat too much and/or I pollute my water with too much food. I am thinking this must be a common problem. How do you deal with it?