Deep Sand Bed for a pond?

[the-obstacle]

I've got a friend who doesn't run the pond filter on the pond he inherited when he bought his house because the running water noise drives him nuts. Because of this he has zero mechanical and very little bio filtration (the only bio being the 3 or 4 water lily plants he has in little pots) and I was wondering if a DSB would work in such an environment?

I would set up the DSB in a tupperware style container with as much surface area as possible as there are upwards of 50 goldfish in this 1.2m wide pond and I'd really like to not see them floating in summer when the heat makes the ammonia peak again.

I have plenty of ramshorn and trumpet snails that I could seed the bed with but not sure they'd survive the pond temperatures. Could also put some shrimp in there but I suspect most would become food.

So, good idea? no? why? why not? alternatives?

thanks in advance

[spoon]

perhaps take the fountain attachment off the pond filter and have the outlet under water but pointing up at the surface for agitation but no running water sound

[the-obstacle]

The only return pipe feeds the waterfall feature hence the noise. He disconnected the actual filter too so it's just a pump running water up to the waterfall which he turns on for special occasions because it looks nice (but turns it off as soon as he can).