Best Substrate For Goldfish?

[catxx]

i'm helping a colleague of mine upgrade her (now leaking) 12 gallon to a 20 gallon(ish) tank (it's still going to be overstocked, but better than the 12 gallon). There's 3 commons and 2 fancies (yes i know, i've told her it's a bad mix, and hope to convince her to rehome the commons and keep the fancies).

The biggest is 5" and the smallest 3". I've seen them snuffling around their gravel and picking it up in their mouths, i witnessed one pick a bit up and take an alarming long while trying to spit it back out again. It's quite chunky stone gravel, 1cm ish pieces.

Therefore, what's the best for goldfish? I've never kept them, but i imagine them eating their gravel can only end badly.

 

[black angel]

Goldies love nothing better than rooting through gravel.
Make sure its pea gravel or gravel so big they cant pick it up.
A lot of people go bare bottomed Thats the tank not them.
If she goes bare then she can add a few river stones.
Another way is sand. Goldies will root around in it and they might push it up into the filter but at least theres no danger of it getting stuck in the throat.
If it were my tank, I would go bare with a few river rocks.

 

[Tokis-Phoenix]

I prefer sand substrate a lot more with goldfish- they love to sift around in it looking for food. Because it is also a lot finer than gravel, a lot less waste gets trapped in sand than it does in gravel as well, so keeping the tank cleaner is easier.