I know that a small fahaka likes to burry itself in the sand.
On the other hand, these fish grow very quick so the advise is to put them in a large tank even when small. But sand in a large tank is a pain to maintain. So the question is: is it necessary for a small fahaka to have a sand substrate? I really would like to avoid having gravel with a part of sand too.
My Puffers: Puffers I have kept: T lineatus T miurus A modestus T biocellatus C valentini C coranata C papuan C lorteti DPs suvattii burrfish T niphobles
I keep sand with mine. He doesn't bury, it isn't too hard to clean, and it's great to watch him hunt food by spitting in it. When he sleeps at night you can see the depressions he "digs" to sleep in them as well.
In th long run you will be better with gravel. Much easier to clean and without the risks.
Fahaka at any age willl be able to bury in fine gravel should they wish.
Mine did it at a very young age then stop for a year.
At 14+" he has started again.
Some call it a product of a mis-spent youth, I call it Rock n Roll !
Mine had sand as substrate since she was a tiny and sickly head & tail.
Never ONCE attempted to bury herself... (All that hassle for nothing.)
Has fine gravel now.