One way to slow down the poop rate of goldfish is to feed them more often but not as much with each feeding. Goldfish have very short digestive tracts and almost no stomach at all, so what goes in pretty much comes out the other end rather quickly.
They are BIG fish so they need lots of food which is why they will forage all the time, munch on plants, etc., but I've found that when I feed mine 3-4 smaller meals on the days when I'm home all day, the fish do not have as much visible poop... compared to how some goldfish will have 1"+ long poops coming out after they eat. This will take some experimenting on the fish keepers part as to how much to feed so that the food stays inside of them longer... and thus be processed so the fish get more nutrition from the food... instead of it being forced out the other end.
The fish don't seem to munch on the plants as much when they get feedings more often either so that's a plus. Someone mentioned floating plants and I agree that floating Anacharis will greatly help with reducing nitrates since the Ancharis will grow faster when it's floating since it's up closer to the light, it can get CO2 from the surface air and still suck up nutrients from the water. It's also harder for the fish to munch on the Anacharis when it's floating compared to when it's planted since they can't tug on it as easily... as it just moves with them. My goldfish leave my BIG crypt plant alone completely. I have to trim it back regularly or it grows to the size of a basketball or larger and doesn't leave much room for the fish to swim in the front or back... and that's with a 48" x 18" footprint.
Goldfish keepers pretty much know that the poop is often the same color as whatever they just ate, which further proves that it's not being processed much while inside the fish for a short period of time. I know the fish poop must still have a large amount of nutritional value as I've seen my Mystery Snails munching on it before... after the goldfish pigged out on some blanched Zuchini slices and the poop was pretty yellow when it came out. EWWWWW!!!... but the Mystery Snails didn't seem to mind. LOL
They are BIG fish so they need lots of food which is why they will forage all the time, munch on plants, etc., but I've found that when I feed mine 3-4 smaller meals on the days when I'm home all day, the fish do not have as much visible poop... compared to how some goldfish will have 1"+ long poops coming out after they eat. This will take some experimenting on the fish keepers part as to how much to feed so that the food stays inside of them longer... and thus be processed so the fish get more nutrition from the food... instead of it being forced out the other end.
The fish don't seem to munch on the plants as much when they get feedings more often either so that's a plus. Someone mentioned floating plants and I agree that floating Anacharis will greatly help with reducing nitrates since the Ancharis will grow faster when it's floating since it's up closer to the light, it can get CO2 from the surface air and still suck up nutrients from the water. It's also harder for the fish to munch on the Anacharis when it's floating compared to when it's planted since they can't tug on it as easily... as it just moves with them. My goldfish leave my BIG crypt plant alone completely. I have to trim it back regularly or it grows to the size of a basketball or larger and doesn't leave much room for the fish to swim in the front or back... and that's with a 48" x 18" footprint.
Goldfish keepers pretty much know that the poop is often the same color as whatever they just ate, which further proves that it's not being processed much while inside the fish for a short period of time. I know the fish poop must still have a large amount of nutritional value as I've seen my Mystery Snails munching on it before... after the goldfish pigged out on some blanched Zuchini slices and the poop was pretty yellow when it came out. EWWWWW!!!... but the Mystery Snails didn't seem to mind. LOL