I think that the 100L tank is a great idea. It would be a great size for just your betta or if you decided to try him tankmates or if you wanted to divide it for more than one betta. In my opinion getting as big as you can is the best way to do things just because you have more options with a bigger tank.
I don't think that any of your options are too tall for a betta, The really tall tanks like ones with sides of around 20in + are not what I recommend for bettas but they would still be ok as long as they were able to get to the surface for air.
I don't think that any of your options are too tall for a betta, The really tall tanks like ones with sides of around 20in + are not what I recommend for bettas but they would still be ok as long as they were able to get to the surface for air.
