Keeping Track of Fish Feeding

I have grandkids that love to feed my fish, and a husband that does too. The problem is that the fish will eat as many times as you feed them! The water dirties very quickly too from non eaten food. What I came up with is a piece of paper with two circles on it.

If you feed the fish in the morning, you cover that up exposing the feed me at night time circle.

At night, you do the same re-exposing the morning circle. See no more wasted food and the fish get fed twice a day instead of four or five times.