When filling the tank with water, you have three options.

The first option is using tap water. It is generally safe for your betta fish, but should be left standing for 24 hours in order to condition it and bring it to room temperature. If your city has especially hard water, you may want water treatment chemicals to remove chlorine and other contaminants.

The second option is using bottled water. It varies as much as tap water does, and if you choose to use it, be sure to stick to one particular brand. If you do decide to change brands, then gradually change it by adding a bit of the new water to the old water over a couple of days. Using betta conditioners is still a good idea.

The third option should be avoided: using distilled water.

You should measure the PH level of your water source, and adjust it they way betta fish prefer. Although betta fish can manage in water that is between 6.5 and 7.5, try to make it as close to neutral water as possible (7.0).

The ideal water temperature for betta is between 72 and 82 degrees Fahrenheit (that's 22-27 degrees Celcius). Betta can adapt to lower or higher temperatures as well as long as the change is gradual. One way to tell if the water is too hot or too cold is by watching the betta fish's behavior. A sluggish, listless fish is likely too cold and a hyperactive fish (unless it is feeding time) indicates water that is too hot.

Gravel and plants
Betta fish likes to rest on the leaves, while people find it more attractive when a tank or bowl is filled with gravel. So if you want to make the fish and the people more comfy, you may want to consider buying gravel and plants for aquarium. Ordinary rocks from the street will not do, I tell you. And remember, before adding the gravel to the aquarium, rinse it in a separate container, repeat changing the water out until it is clear.

Tank maintenance
If your tank is smaller than one gallon, then change 100% of the water once a day or at least 3 times a week. If you have larger tanks, do partial water changes of 25% of water a week. Be sure to siphon or vacuum your gravel when you change your water.

Last thing, the water does not need to be aerated. Why? Because the betta fish breathes at the surface of the water. Aeration and circulation may create too much flow for your betta, and they're not accustomed to having to swim very hard.