Easy To Clean Decorations For Large Goldfish

My parents have 2 large tanks where they keep their pond goldfish for the winter. There are about 40 goldfish and the tanks are a 75 gallon and a 125 gallon. There are 3 filters per tank and the water is always crystal clear. Theres gravel but I feel bad that's there's no decorations or anything. Do goldfish need decorations? If so, are there any decorations that are easy to clean and are soft enough not to hurt their tails?

 

I'm sure they'd appreciate having some interest in their tanks but neither do you want to take away any water volume or swimming space.

If you did want decor I would choose rounded river rocks.

If you want to keep the goldfish amused however, what about floating a couple of ping pong balls in the tank? Too big to swallow, easy to clean, and the fish can move them around easily

 

You could grow amazon swords. The fish would munch on them and they'd add beauty to the tank

 

Duckweed? Unless the filter would suck it up.

 

Duckweed? Unless the filter would suck it up.

Tried that, but the fish ate it within 30 seconds