i read it correctly. still don't think it's very useful as a rule...it doesn't really work for anything that gets larger than a couple inchesIt's actually very useful. You have to consider the adult size of the fish when using it though. It's not 1 gallon for every 1 inch fish. It's 1 gallon per inch of fish.
It's not a hard and fast rule though. For example, you're not going to put a 5" cichlid in a 5 gallon tank and expect it to survive very long. It does work for stocking purposes in example cardinal tetras are about an inch or so give or take as adults so I could put 5 in 5 gallons. With proper maintenance and filtration, they'd most likely flourish.
I'm pretty sure the tank will have a hood, but either way all fish can jump, so it's not just bettas at risk for jumping to their deaths. Glowlights and black neons grow too big around 2 inches long for one fish, and they prefer to be in schools.Was he ever a fisherman? Catfish might interest him. I'd also suggest simple tetras, maybe colorful glowlights (if dad can see color), or black neons. While betas are interesting, if [when?] it jumped out and if it died, dad would feel bad.
The opportunity to watch something alive and lively (that's not TV) may perk your dad up.
Very good idea. Dwarf Puffers are amongst the most intelligent fish I've ever dealt with. They're fun to watch and fearless. They'll swim up to your finger from day one. If you want some action-entertainment, get some tiny snails from your LFS and the Dwarf Puffer will hunt them. Nothing's more fun to watch. General rule is 1 Dwarf Puffer per 5G.I'd go with a Dwarf Puffer and an oto... The puffer should be very intereactive with him and the oto would be good for any algae that would grow.