I agree; I also think CritterNut brought up a good point. You can't go all out on a smaller tank, where as, with a bigger tanks, you can give it a theme and what not. Obviously not incredibly important to the well being of our fish friends, but it's just a nice little aside for us keepers. :)
tank care is more important then size IMO, within reason of course. I wouldn't go any smaller then a 1 gallon since finding a way to heat it would be a big problem. Personally, I like 5 gallons for one betta - but I have everything from 1 gallon up to 20 gallons.
As for a minumum size - for a newbie - I would say 3 gallons since they are probably unaware of water chemistry, cycling, ect. But for someone who knows what they are doing - 1 gallon minimum.
If its a choice between dying in a cup or living in a matintained .5 gallon, obviously the .5 is a much better choice...
would you rather be in a clean dorm room with fresh air and food but little space OR in a big apartment that is full of mold and toxins? I actually had a large apartment that was full of mold, nothing worked, the flooe was literally rotted out and the place should of been condemed. I moved into an apartment that was 250 square feet total size (think dorm room with a stove/fridge and bathroom) and that was 100X better. Keep in mind I had a dog, chinchilla and 23 bettas in this tiny space.
I'm the biggest plant fan, and when you have plants, magic happens. You can keep a fish alive and healthy in a quarter gallon jar. When you have plants, 1 gallon tanks become almost zero maintenance :)
So to me, the question isn't "what tank size can I keep a betta fish alive in" but rather, "what tank size is *ethical* for my fish?"
I believe the correlation between ethical fish keeping and tank size largely varies from fish to fish. Especially for the betta fish due to their unique personalities. To me, putting a nervous tail biter in a 10 gallon can be equally as cruel as homing a hyperactive plakat in a 1 gallon. A fish who needs a school should be given a school and the tank size suitable for their schooling activities, and a fish who demands territory should be given adequate space to reign over. In my opinion, the size of the tank should depend on the individual betta's personality.
That said, what would I tell a beginner fish keeper who just got home with a carnival won bettafish? I would tell them that five gallons and above is best and to go no lower than 1 gallon. They have their own fish keeping adventure to start out on, we can only point them in the right direction by sharing our own experiences. Those who care for these little lives will do the best to keep them alive and happy, While those who couldn't care less about the happiness of the fish, will opt for the cheapest way out.
At the end of the day, it's impossible for me to change the way someone thinks or the way they act. It makes even less sense to become upset about it. As long as I can keep my own fishes happy, I'm satisfied. Because to me, this hobby is meant to be a gift, not a headache :)
All of my tanks are planted. I have one veiltail betta I keep in a 2 gallon aquaeon evolve 2 gallon, he has plants a pvc hiding place and a leaf hammock, he sits basically right next to me I have one of those shelf lamps his tank fits perfectly on. He loves the intake grate for the pump/sump area he rests right there and stares at me, he is my most aggressive betta and is pretty silly he flares at me and likes to play, he is perfectly happy in his 2 gallon, he used to be in a 1.5 gallon till I ran into his aquaeon for 25 dollars at petco, it is planted with enough plants that it only needs a water change like every 1-2 months, I test the water weekly to be safe, it boils down to the level of care vs the size of the tank, to those who do not have a planted tank you are missing out
Tank size can get quite heated on both sides when it comes to bettas.
If you are experienced and you know you can keep up with the MINIMUM water changes, then by all means, keep doing what you're doing. I'm not going to pontificate how you should change your fish keeping habits.
On the other hand, if you are new to fish keeping or new to bettas, I offer this warning:
Sooner or later you will likely skip a WC. In a one-gallon tank with a betta, even one that's heavily-planted with natural plants to mitigate the ammonia pollution, somewhere around 10 days your betta is likely going to start losing the tips of his fins. I know this bit from personal experience, and that's why I moved away from 1 gallon tanks. Eventually he will die a slow, painful death if the water is left unchanged. The ammonia will build up to a point where he suffocates and dies.
I'd also like to touch on the inherent risk involved with a 100% WC. After several years with no bad experiences netting fish, I had a beautiful Dalmatian betta jump the net net when I was attempting to put him in the cup. One more flop and he was in a small pool of dish detergent. I did my best but he did not pull through. I share this as a warning, hoping someone can learn from my mistakes. Your WC should be done in a clean, uncluttered area, like a clear dining table. Sooner or later you will drop a fish, so make sure there's nothing harmful around. Lastly there's water to consider. Make sure you acclimate him to the new water as you would a fish that you just brought home from the store: let him sit in a bag in the newly-changed water and drip small amounts of the new water into the bag so he can get used to it. You never know when your tap water is going to have an unexpected pH swing which could shock him to death.
Finally, again mostly for the beginner here, I'm including a video I made of a full WC from back when I had 1 gallon tanks. It's about a 10 minute ordeal, even after you have a system down and everything ready. 10 minutes per week per tank.
In my experience, an oactively growing heavily planted tank is unlikely to show ammonia nitrite or nitrates. The tank must be established and under proper lighting ... preferably running off a timer~
However getting this right will take time. I it will be a while until a newcomer to the hobby will truly understand the capabilities and limitations of their own setup :)
I often go on a one or two week vacation where I leave my betta home alone, he does very well for himself :) He does bite his tail when it gets too long, I don't know whether that counts as him losing his fins XD
I'd also like to point out, Don't net Betta's or any fish if you can help it. Instead, use a plastic cup like the ones they come in or red solo cups even! And then scoop them out, less stressful for your and your fish and you're less likely to drop your fish
Red solo cups lol love it. I didn't know bout the netting but want to share a funny story. I was removing some water with a measuring cup, the tank light was off. Just as I was about to pour the water in the sink there sushi sat in the measuring cup. Close call but it was too funny. The pissed off look was priceless. Point of story? Check cup for fish lol