Hi! I've got one of these. Mine's the front one and he's called Mushroom

Had him 9 months or so now.
He lives in a 4ft tank with an external filter. The salinity is 1.020, and it's taken nearly all 9 months to get to that. I kept him in 1.015 for a fair time before doing the final raise gradually to 1.020. I'm sticking with 1.020 personally, I emailed PFK magazine and got a reply from neil monks whose recommendation was 1.015-8, so I'm staying somewhere around that since he knows what he's on about when it comes to puffs!
Temperature-wise, everything I've read suggests 15-18 degrees. However, Mushroom has reacted badly to every attempt I've made to drop his temps. I keep him at 20 degrees at the moment. (I live in England, so a chiller isn't needed at all for me, it's always rainy and cold here!! lol) I would drop your guy's temps gradually, and make your mind up based on their behavior what temp to go for. 20 degrees should make a good starting point.
Soft sand, imo, is a must. Mushroom buries himself if he's spooked and always buries after he's eaten. He needs a lot of floor space to do that, so decor is all along the back and side walls of the tank.
I don't use live rock, firstly because I haven't yet worked out how to cure it to the right sg and temps!! lol. Secondly, Mushroom is clumsy and I don't trust him not to try to bury himself IN the rock and injure himself. If you want to use live rock, what I've been thinking about doing is crushing some to put in the filter, so that might be worth looking into.
I have him on cockles as a staple, with bloodworm fairly often too. He goes mad for the tetra fresh delica sachets! Everything he eats is soaked in Waterlife Vitazin vitamin supplement, which imo is a must.
Bit of a wierd one, but Locusts according to everything I've found are very nutritious and would make a good diet, however, feeding a live locust is an experience I don't care to repeat... Do some research if you want to consider it, but it's not pleasant to see!!
Have a read up on thaiminaese (oh someone spell that right for me please!! lol) his foods have to be thaimanese free for the main part. Mussels are good as an odd treat, but very, very rarely. Mushroom hasn't had one for over a month.
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Sorry for the long post! I love these guys

They're amazing little fish if you can get their care right, and getting their care right is a work in progress! So defo give it your best shot. No one can really say at the moment what the best long term care is, so it's just people like us experimenting that'll figure that one out. So far so good, my little guy is very healthy, so hopefully I'm getting something right, but time will tell.
Edit: I said I'd had Mushroom 7 months, it's not, it's 9 months, so edited. Doesn't feel that long! Not too sure where I got 7 from...