A ten year old should have a shell of 25cm which is roughly 10'', so mines doing just fine, thanks.

You didn'y say prawns you said fish. Mine does eat meat just in very small offered amounts

Regardless of how much waste he produces the nitogen cycle will turn this to nitrate, no two ways about it, trust me i have a degree in chemistry.

You go and pee and poo in a pool and it will turn to nitrate trust me.

As for tank size, the tank he is now is more than adequate for him and in a year or two when he is bigger he will be moved to larger accomadation.

It would seem you have a little bee in your bonnet purely because you don't like parrot fish, i could say the same about you keeping arrowanas and rays, so please if you want to have a dig do it about something that you know what you're talking about.