This is not advisable as composition of rain water is nowadays unpredictable.
no because if its a freshwater tank the rain has salt in it
Yes
First make sure if you put tap water in there you put water cleanser in there which can be bought at a pet store. Keep your betta in the bag and float it in the tank for 15 min. then without dumping the bag water in the tank use a net to move your betta to the tank.
An intense bushfire would severely warp a plastic rainwater tank.
you can put a betta in a 54 gallon tank
I would definitely not do this. The chemicals from the paint can be extremely toxic to the fish and can possibly be fatal. If you want your betta to stay healthy, do not use paint in their tank!
A betta is best as a solitary fish and it would be better to remove it from your main tank and give it a small tank to itself. You can buy very inexpensive betta tank kits for one betta.
Betta are airbreathers. So long as the ammonia and nitrates are okay, you don't need filters on a Betta tank.
your betta will do just fine in close proximity to the turtle
The bigger the tank, the better. I use my spare 10 gallon on my brine shrimp. I raise them to feed my betta.
A minimal tank size of 2.5 gallons is recommended for a single Betta fish.
put it in a tank with another male betta