Fish, like most creatures will feed until they are "stuffed". Nature has designed hem that way. The reason: in the wild no creature knows when they will get their next meal and so they eat as much as they can,when they can. Survival instinct. We are no different, when you think about it carefully. so overfeeding a fish can be detrimental both to fish and its environment. YOU know when you are next going to feed your fish, but your fish doesn't, so it will consume any food like it was going to be their last. If then you feed it 4 or 6 or even 8 hours later, the fish are going to be half full and trying to stuff more food into itself. As the old saying goes, what goes in must come out. So unless you have a super over efficient filtration unit, the bio-load will soon reach its optimum efficiency and start to dump pollutants, which are invisible to the naked eye back into the tank. This will cause all kinds of problems. It is alway advisable to have a basic water test kit to hand.
My advise for what its worth is you can kill your fish with kindness.
It's best to feed them like Morrgan suggests, and maybe to not feed them at all for a day or two every now and then. Fish will come to no harm if left for up to 4 days without food as long as they are healthy and the water is in perfect condition.
OK We all have heard the constant warnings not to sicken fish by overfeeding. But, is it the consumption that hurts them, or the uneaten food turning toxic in the water? I have 2 male plattys that want to eat like teenage boys! Every time I put food, they act ravenous. Is it ok to feed them what they want to eat, even if it seems a bit much? They never leave a speck uneaten. (After all, who can really understand or satisfy teenage boys?) 
Thanks friends.
