soft water at 78-84 degrees
If you wish to have healthy Bettas then they need clean tropical water, a pH of about 6.8 a temperature about 78F and a minimum of 3 gallons of water to live in. They also need at least 50% of their water changed weekly.
Chlorine will kill just about anything so yes it has to be removed. Because chlorine is a gas it will evaporate off from tap water given time, so provided the water is allowed to stand overnight there is no need to use chemicals to remove it.
If you meant to say oxygen, then yes some fish, like bettas, swim to the top to get air while others use their gills to get air from the water they live in, like goldfish.
Doesn't really matter what kind of energy source you use, water isn't an efficient media to transmit electricity through.
Yes, bettas can go blind due to various factors such as poor water quality, old age, or genetic conditions. Signs of blindness in bettas include difficulty finding food, bumping into objects in the tank, or not responding to movement outside the tank. Providing a clean and enriched environment can help prevent blindness in bettas.
Betas are labyrinth fish, meaning they use both their gills to gain oxygen from the water, and a labyrinth organ in their head that lets them breath from the air. They do not need an air bubbler, but they DO need filtration and properly heated water (80 to 86 degrees)
Water is not a good stain-remover, you need chemicals or cleaners. However, if you really need to, carbonated water should do the trick better than regular water. It will not remove the stain completely though.
Any water resistant indoor laqure will do it.
Just because a Betta can live in cramped conditions for a while, does not make a tiny aquabox a good or suitable container to keep one in. The absolute minimum size of tank a Betta should be kept is one that is nominally rated as a 3 gallon tank. The reason for this is that once adjustments to the amount of water it contains when in use is a little over 2 gallons. The basic rule for keeping any kind of fish is "1 inch of fish needs a minimum of 1 gallon of water". Bettas grow to around 2 inches body length. So you need a tank that actually contains a minimum of 2 gallons of water.
drinking water and rain water
always use copper for any kind of water installation
hard water.