Hi, truckasauras123,
congrats on the coming betta acquisition and on soliciting advice on the care issues.
I'm in with the heater contigent, which can also produce an immediate improvement in colouration as a visual demonstration of the difference it makes - and most of mine love Hikari Micro Wafers.
Some still wolf down Betta Max flakes, but you'll likely find yours get progressively fussier the longer you've had them and may sometimes eat while at other times ignore various flakes and pellets, although bloodworms and the weekly pea feed are always popular with mine.
You never know what their response to various foods may be, or what it may change to.
Confetti, one of my crowntails, initially liked the Micro Wafers I fed a couple of times a week and I assumed he was continuing to eat them.
But maybe a couple of times a week I started to find disgusting-looking brown foam in his bubblenest, which was covered by glass, so that nothing could possibly have dropped in from overhead or consistently floated to that area.
No smell, the emergency waterchanges showed crystal clear water in the white dump bucket, and when dipped out, the brown foam looked like nothing I'd ever seen - of course, I was focused on and panicking over it being some horrible bacterial thing or very odd rotted plant (or possibly insect) matter, as a murderous plant disease is present in that tank, and I do plan to ditch the substrate and redo it as a Walstad anyway, once I can finally obtain some decent, fine dark gravel to cap the earth.
But this appeared overnight - not enough time for such through rotting and didn't look right anyway.
It took me about a week and a half to figure out what everybody else just did immediately - he was nurturing the pellets and trying to keep them up in his bubblenest...
How sad.
But I suppose he could possibly see the babe across the way, and was perhaps wooing her in the only way possible.
Since he's not big on flakes or most other things and can't eat nothing but the bloodworms and peas he does love, he's a bit tricky to feed, as I've quit putting pellets in since he evidently wasn't eating them and his best efforts were raising a fine ammonia source.
But he does now seem to be eating the flakes again, anyway.
And I haven't found those in his nest, yet, either.
As far as tank size goes, I'd say it depends on the betta, as they're definite individuals.
I have one in a 15, has a great time non-stop and I'd never want to see him in anything smaller, and have been planning to move another, (currently in a 10 gal,) into a 15 for some time, although this has been delayed due to illness...
I have another in a 10 gal (that's Confetti - who couldn't swim when I got him, having no membrane at all on his swim fins - and was heartbreakingly terrified of the Daily Syphon and Evil Hand Team searching the bottom, obviously to devour him, because he could only slowly and frantically squirm away on his belly - and had to perch on a mid-water-floating ice-cream bucket in a bare-bottomed 5 gal. Q tank to bubblenest and easily reach surface, but swims like a calm, brave fish now) and one in a 5 gal and 2 bettas (one being my only female, bought as a male) in 'emergency' 3 gallon tanks.
I'm not super happy about that, but they seem to be OK with it as it'll be the biggest they've known since grow-out, and are both very small fish, (thought 'babies' but apparently same age as the much larger others, only stunted) bought with health issues, who've grown very little, esp. my girl, who almost certainly won't be able to enter my future 15 gallon sorority tank after all, due to the potential for unknown disease transmission ...
Long-finned bettas are more likely to blow their tails in larger tanks, as they often tend to be more active given more places to go and things to see, but between the potential extremes, I'd rather have an active, interested betta with a 'bald' rump or one in various stages of regrowth than a bored, inactive and potentially constipated/overweight betta with perfect finnage, which is lucky under the circs. since I do have one like that...
I'd say one of the big things about bettas in little tanks is that they can keep busy and amused if they have lots of plants to swim through and between.
It effectively makes the tank 'bigger' because there's somewhere to swim to and things to investigate en route: personally, I'd feel terrible keeping an intelligent fish like a betta long-term in an 'empty', unchanging tank...
Just my feelings on the subject, and observations based on the pathetically few bettas I currently have.
I hope to considerably extend my ability to observe different betta's various personality and other traits down the road.
Purely out of scientific interest, of course, as I'm clearly not a betta addict with only the 6.
And I'm sure you won't be either, truckasauras123 - isn't the definition of a betta addict something over 2 dozen?
EDIT: I absolutely agree with you, truckasauras123 - 100% water changes are stressful for the fish, and while they may be necessary in a very small container, in any cycled tank, the nitrifying bacteria will be regularly starved as well by these, having their entire food source removed, so that the tank may never cycle properly at all while this continues.
People forget biological filtration is based on a natural process, with living creatures dependent on, and propagating to, the food levels.
The ammonia and nitrites so toxic to our fish are food for various of these bacteria, and without these 'nutrients' they die off.
It's better to conduct smaller changes more frequently, if possible, than very large ones, although under some circumstance unavoidable.
And a good percentage of healthy plant growth will do more for the water quality than almost anything else, both by directly consuming ammonia as it forms, and by providing surface for beneficial bacteria to grow.