While I don't know about Greys and other larger parrots, when a chick is eating only formula, their poop is that strange formula like consistency. Eventually they start pooping the solids floating in the liquid.
If your bird is only pooping liquid, it could mean they are not getting enough food, if they are ony eating formula then that would mean the formula is too thin.
Double check your formula consistency and temperatures. If everything is as it should be, you could take a picture of the poops and send it to your vet to see if they think you should take the little guy in.
@BrianB @Jan @Macawnutz