Why is your pregnant platy pooping alot?

You may be overfeeding it, Fish are often given too much food even if they will eat it. It is recommended you feed them however much they can eat in about 5 minutes only once or twice a day. Be sure to clear out uneaten food from the tank as it may cause the water to get cloudy. Also if you are talking about goldfish they are in general just a dirty fish that does that a lot.