This should be 2 to 10 gallons in size. I have used both a 3 gallon clear critter keeper and a plastic “shoebox” that was 2 gallons in size as well as traditional glass aquariums.
For the most part, bettas are not picky about pH or hardness. My pH is high (over 8) and my water is also very hard. At one point I had trouble with the males being able to build bubble nests. It was temporary but I have now gotten in the habit of adding one quart of distilled water for every 2 gallons of tap water. This helps soften the water a little. The water should be 6-8″ in height. I tend to fill a bit higher than this so that I can siphon the bottom right before I let the fish spawn and it allows for one last cleaning. When first filling up the aquarium, make sure to use de-chlorinator as chlorine/chloramines may harm or kill bettas.
Bettas are encouraged to breed when an almond leaf or two is placed on the water’s surface. I have also used Atison Betta Spa successfully and the dosage for that product is 5ml per gallon of water. If you do not add almond leaves, it is advisable to cut a small styrofoam cup in half length wise to form a “cave” for the male to build his nest under. I like the cup myself because it makes it easy to gently/slowly move the nest when absolutely necessary if the aquarium becomes contaminated in some way or if I need to move the nest away from some plants so that the eggs will be easier for the male to care for. The cup should be placed at one end of the aquarium away from live or fake plants.
A submersible heater should be added and suction cupped about an inch or two above the bottom of the aquarium. I prefer the old style glass thermometers because they seem more accurate. That is only my opinion so you could also try a stick on external thermometer if you prefer. The temperature should be between 80 and 82 degrees Fahrenheit.
Important! Set up the aquarium at least a couple of days before you intend to spawn the fish. Heaters can and do malfunction. If the aquarium is too cold the fish probably will not spawn for you. If too hot your fish may be cooked!
Live plants are a must for several reasons. They help prevent ammonia spikes since there is often not a filter in a spawning aquarium. They offer a place for the female to hide from male aggression before and after spawning. They offer a place for infusoria to develop as a first fry food. Plants assist in keeping the water cleaner by absorbing toxins.
Spawning aquariums should be “bare bottom”– no gravel or decorations of any kind. This allows the male and often the female to easily find the eggs after each embrace and place them in the nest.
It is very important to have a cover over the aquarium. It prevents the fry from becoming chilled, keeps the temperature even, keeps the adults (especially the female) from jumping out during the spawning process. The cover can be a traditional aquarium cover with light, or something as simple as clear plastic wrap.
Once the fish spawn, a light will have to be on 24/7 until the fry are free swimming. If the aquarium is somewhere where it will disrupt human sleep, consider using a small LED aquarium light. They are not super bright, but are sufficient for the male to see the eggs and care for hatched fry.