It's not necessary, but it will provide warmth to your betta which will raise its immune response and keep it happier. If you're in a tropical climate, (lets say, Philippines) you won't probably need a heater due to the warmth but you will if it's not stable. I have a highly recommended heater in my 3.5, it never overheats.
It's called the Hydor THEO.
I also recommend Visi-Therms and Eheim Jager heaters.
Your betta will live a happier, healthier life with a heater. Get an adjustable one so you can be prepared for any needed increase or decrease.
I also recommend Visi-Therms and Eheim Jager heaters.
Your betta will live a happier, healthier life with a heater. Get an adjustable one so you can be prepared for any needed increase or decrease.