My Val Bertie has had a variety of sleepspots (do all puffers sleep as much as he does -- Bertie sleeps more hours than I do!). He (yes, I'm leaning towards male as the gender now...) first simply slept on the floor of the tank, then started to anchor himself wedged into the corner of the tank (does he put out some kind of glue to stay there so firmly all night or something?). Next he started to wedge himself between the top of the heater and the control knob and that worked for a while, until...
In the tank (it's a 30 gallon quarantine tank undergoing hypo) was also a lone pyjama cardinal (Judy) that apparently decided, being a schooling fish, that for lack of a better school, Bertie would do. For a bit, she'd butt Bertie, gently, but still, it made me nervous. Bertie simply ignored her and went about his business (I've thought of Bertie as female for so long, forgive me if I mess up genders...). Until, one morning, I was watching Bertie sleep on the heater and noticed Judy "divebomb" Bertie and knock him off his perch. After a bit more chatting, Judy's desire to school was decided on and two more pj's were added to let her fulfill her wishes and hopefully leave Bertie alone. Oh, and I added a veggie clip near the top of the tank in hopes that Bertie would sleep on it a la Diddy (thanks, Bonnie!...) and no longer be dive-bomb-able. (Worked, too, now Bertie regularly sleeps in the crevice between clip and tank wall.)
You figured, right, didn't quite work out like we'd hoped. They stopped butting Bertie and focused on each other, but still... Bertie's perch, well, I watched the Judies play "Puffer tipping" three times in a row one morning (Bertie would swim around for about five minutes after they tipped her and then go back to bed and a few minutes later get tipped again)and decided it was time to separate them before things escalated. And then, there's more...
There was going to be one more night together, just didn't get around to figure who was going where yet, and all the lights were out in the room besides Bertie's tank, and apparently that makes a mirror in the front glass. Bertie puffed a few times at the front glass (that is a really freaky thing to watch, btw), I ran for the lights when I finally figured out what was going on, and Bertie butted all three pj's just like they'd butted her; you could just about hear him saying, "Get out of my way!". And the PJ's did, and now they follow Bertie around the tank from a respectful distance and Bertie herds them into a corner at night, and they seem to stay where he puts them until he starts swimming around in the morning. (Four nights running, now...)
'Course, this all could be my imagination, anthropomorphizing and all, but still... Bertie seems to have gone back to his docile, unaffected, non-butting self, and I'm left wondering if all of this can possibly be a reasonable explanation.