I give my father's goldfish duckweed. Now my father picked up on the trick and takes my duckweed to feed his goldfish! There's plenty of the stuff and no real harmful effects for eating too much, just a little extra fiber, vitamins and protein. Feeding too much pellet foods can cause swimbladder problems as the intestinal tracts get clogged up and put pressure on the fragile swimbladder. No real harm in eating too much, just need to make sure they pass it out. It wouldn't benefit them much if all that food they eat don't get digested though. I guess everyone's who's had different types of goldfish would've had this problem but it doesn't do much harm as long as there's enough filtration and variety of foods.

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