What else is in the 60L? You have to be careful what you keep with bettas.
Generally the best diet is a formulated betta pellet and the best (in my opinion, which I share with most of the betta board posters) is Hikari betta bio-gold. It's very expensive as fish food goes, but if you only have a few bettas it doesn't really add up... I have about twelve and I still manage to feed it almost exclusively. It's best to vary the diet with treats like bloodworms (frozen is best but freeze dried is okay) and other frozen/dried food like daphnia. It's also a good idea to have one fast day per week when you feed nothing, and one day when you feed a frozen pea. Don't kick yourself if the betta won't eat them - a lot of mine will not touch peas. They are good for their digestion, but a lot of them don't like peas.
What you see in the videos is cruelty through ignorance. People like the idea that they can keep a fish as a table centrepiece with virtually no experience and no work whatsoever, and that they can have fish despite having limited time and space. Therefore pet stores perpetuate this idea because it results in sales. They have a lot of stories to make it seem less cruel to Average Joe, because it's undeniably wrong. Children who see them in cups for the first time react with horror and outrage - until one of the pet store staff dutifully explains why it's better to keep them that way, and recruits yet another betta keeper to perpetuate the cycle of abuse.
The stories I'm talking about are the ones that get repeated on here every so often and make experienced betta keepers cringe (or start throwing things at the screen). Things like 'bettas live in buffalo footprints in the wild' (Rubbish. They survive in them through the winter if water dries up. Normally, they live in rice paddies - knee deep.) 'Bettas hate big tanks, it's cruel to keep them in big spaces because they feel they have to patrol it all'. (Rubbish. A five or so gallon tank is perfect, and if they decide the space is too big, they will claim one end of the tank as 'theirs' and patrol that.)
Yes, bettas are tropicals, and they DO need heaters. Yes, the cold and the constant exposure to ammonia does serious damage, and usually reduces the lifespan by a horrifying amount - even rescues removed from this environment at six to eight months only live for about 1-2 years as opposed to 4 years which is often achieved by 'breeder' bettas that have always been well cared for. Six years is not unheard of.
Filtration is not the only option (personally I use ammo-lock) but ammonia does as much damage to bettas as it does to all fish. They are just better at surviving it.
