For a 3 gallon tank the heater needs to be a 25 watt heater and the one under the gravel will have him too hot. A betta does well at a constant 78 to 80 degrees but not much variation from that. Less than that and he is going to be susceptible to the cool water diseases like
ICH, Velvet and Finrot. More than that unless he is being treated temporarily for Ich and he is living at too fast a speed. Bettas lives are shortened when they are kept in too warm a water (over 80 degrees) for long periods of time. They are definitely tropical fish and have a very narrow allowable frame of optimum conditions to live in.
The heater I would recommend would be the Visi-therm Stealth heater in a 25 watt size as they are not more expensive than the others right now and are the most accurate and dependable heaters to my knowledge. They have lifetime warranties so keep the box and receipt if you purchase one to maintain your warranty.
http://www.drsfostersmith.com/produc...0&pcatid=12060
The food that I recommend for the best in foods are the same ones for the most part. For baby fish I recommend:
3 pellets of this two times a day:
http://www.drsfostersmith.com/produc...m?pcatid=15530
and
a sprinkle of this one time a day:
Freeze-dried Daphnia
http://www.drsfostersmith.com/produc...fm?pcatid=4279
Then for a little extra protection:
http://www.drsfostersmith.com/produc...fm?pcatid=4998
these are just vitamins for him and will give him a better immune system and better healing capability if he does get sick. (if you order be sure to purchase the Freshwater type)
Just my

. Welcome to Fishlore.com and hope this helps.
Rose
