The Puffer Forum

Prolapsed rectum: treat with 1 tbsp Epsom salt/10g.

If he's fat & happy, I wouldn't worry about IPs.

Fahaka https://www.pufferfishenthusiastsworldw ... care-sheet

If you use filter media from an established tank, your 20g should have enough bacteria to handle the bioload from 3 tiny puffers diluted in such a large tank. Water changes are never a bad thing.

Give them some time to get used to their surroundings, they blend in fairly well. Do you see them when you feed them?

Totally normal for sleeping. Eating plants, searching for snails. 1/005 is good.

I agree with your fish store. Your SG is fine, no higher. I like 1.005-8.
library/puffers-in-focus/fig8/

You will love them!
https://www.pufferfishenthusiastsworldw ... vancoricus

If you treasure your other fish at all, then YES, I would put the fahaka in a tank by himself! They are proven killers. They are known to go on a hunger strike when moved to a new tank. After a few days of settling in, they may eat live earthworms.

He looks extremely healthy to me, I wouldn't worry about 1 white poop.

Maybe they're not as overgrown as you think then.

This species is a piscivore. Fish are their staple food.

Sand is preferable. You don't have to remove him, just scoop the gravel out with a net.