No. Charcoal bits will harm your betta fish. But you can use deactivated charcoal bits
No, gravel covering the ground of the tank or bowl will do fine. If you can fit them, they might also like an aquarium plant (living or plastic).
totally upto you. i have gravel in my bettas tank.
6inch
No, they are fighting fish. They will kill each other no matter what sex they are.
They sorta can it depends on what color they are and the decorations and gravel. My betta is pure blue and it blends in with the gravel since the gravel is blue and some of the ornaments are blue.
I have always had gravel at the base of my Betta breeding tanks. The male will collect the eggs before they reach the gravel provided the tank has at least 10 inches depth of water.
Any decent quality aquarium store should be able to bring in female betta's for you.
Yes, a betta fish can live in a jar if it is large enough. Gravel can be placed in the jar and it can be a good habitat for this species.
most of the time but with betta fish no they can live at room tepature
my betta bowl has sea glass which is really dull glass so it wont cut itself
If it is like a black clump then its your fishes feaces(crap).clean it out
You should only have 1 fish per gallon of water in a fish tank. I wouldn't put more than 2 or 3 Neon Tetras in a 4 gallon aquarium with 1 Betta.