the deathcetera in my area no longer has bettas in cups, thank jeebus. but last time i was in i did not see any signs informing people of what you could/couldn't do for betta tankmates.
"12gal? Thats way to small to house a school of betta they would kill each other. I yi yi. Always wondered why is it when there in those cup that some places have it in like blue water???"
there is no such thing as a school of betta. even two male bettas in the same tank, even if huge, would most likely find each other, fight each other, and one would end up dead due to injury or ensuing infection.
as for the blue water, it is methylyne blue, a common medication that is supposedly pro-actively used to keep the bettas from getting sick. bullpoop i say. if the betta ain't sick, don't medicate, and if the betta is for sale, it should not be sick to begin with. i've watched the petsmart people unpack a fish shipment and the bettas came in clear water and they added the blue, and didn't even change the water from what they were shipped in. grrrr.... ok, rant over. lol.
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"By the way, what's wrong with keeping them in cups, as long as they keep the water clean? Many betta breeders grow the fry out in small glass jars. Works great. Now, if they aren't changing the water in the cups, I could see how that would be torturous, due to the small volume leading to nasty water in no time."
betta breeders keep them in the cups and jars because they are not housing the bettas long term, they are raising them to sell, hopefully to somebody that will give it at least a 5 gallon long term home. as well, breeders do pretty much daily water changes, and that is one heck of a lot of work!