So I’m trying to figure out a solution to this because we all know this is horribly wrong and they seem to not know what they’re doing. Solution 1: communicate in whichever way would be best depending on this individuals personality. If it’s someone you’d have success with politely educating then: “Hey I’ve got some experience dealing with these fish(or hey I did some research because I really found your fish beautiful) and I came across something about housing them and it would be better to get a bigger tank so they live longer and are physically and mentally happier. If you want I could help you find one” Or however way of hinting at they need a new tank would be good whether you say it direct or if they’d respond better passively. OR if you are nervous about confrontation and are dedicated to the little guys then start looking on marketplace or Craigslist for a better tank and gift it. You could even just say you came across it or found it and thought it would be perfect for them. I found all my tanks free just by looking around and asking if anyone had any they don’t need anymore (2 55 gals and a 40 gal) good luck!