I have a male betta fish that i recently added to my mollie tank and i was wond...
Your male betta will thrive living on his own, or as the only male of the species in a peaceful community aquarium with smaller fish.
A one-gallon aquarium is very small, and only will hold a few fish. The general rule is one inch of fish body length per gallon of water. So a one-gallon aquarium could theoretically only hold one fish that is 1" long. However, several small fish would do okay in that tank, such as your betta and a few mollies. The problem with mollies, platys, and guppies is that they breed readily, and if producing babies they will soon overcrowd the tank. A good mix for a one-gallon aquarium would be one betta, and 3 small schooling fish such as zebra danios or white cloud minnows, and one otocinclus (algae eater). A few live plants and a mystery snail could also be added. If your mollies are all the same gender, you will probably be okay with them, but if not they will breed, and then you are going to need a bigger tank. That is part of the fun of fish keeping, however, as one tank often grows into keeping two or more - usually subsequently bigger ones!
When adding fish to an aquarium, the fish need to be added a few at a time at the beginning. It takes about 4-6 weeks to develop enough beneficial bacteria in an aquarium to break down the fish wastes. New aquariums go through a cycling process where beneficial bacteria "bloom", making the water cloudy. The filtration system will ultimately trap the bacteria, and clear the water. The bacteria will continue to grow in the filter, turning it into a bio-filter. The beneficial bacteria are an important part of maintaining a healthy aquarium. Adding too many fish before the bacteria can build up can be harmful to the fish, and is known as "New Tank Syndrome". Be sure to test the water quality frequently. It is easy to do using a water test strips.
It is always best to quarantine any new fish before adding it to an existing aquarium. This can be done by using a small aquarium with a filter. The filter will not be biologically active if the aquarium is not running constantly, so it will really be for aeration, and you will need to do frequent water tests to check the ammonia level. Ammonia test strips are available at PetSmart. Also, PetSmart offers free water testing. Bring in a container of your aquarium water and the PetSmart associates will test it for you to see the levels of ammonia, nitrite, nitrate, pH, hardness and alkalinity in the water. You can also pick up free guides on fish diseases and on aquarium water quality. If the ammonia level is increasing, perform a partial water change to lower it. After a period of 2-4 weeks, if the new fish in the quarantine tank are active and eating with no signs of disease, then they can be introduced into your aquarium.