Betta fish bloat

Question
I've had my male betta fish for about three months now and he's been perfectly fine the whole time. I got him a new 1.5 gallon tank about 5 days ago (with the little mermaid!) and he's suddenly become pretty bloated. His old tank only had a bubbler and no filter, but the light was stronger and probably kept the water warmer than the light in the new tank. His new tank has a filter and no bubbler, and the light is much dimmer. He's been eating the same food since I got him. I try to feed him every day or every other day. I just noticed his bloat today so I'm not sure how long it has been there, but his scales are not pine cone-ey and he's still very active. Do you know what could be wrong?

Answer
Hi,
He may have swim bladder disease.  This disease is caused by overfeeding, and poor diet which leads to constipation.  If not treated quickly this disease may lead to Dropsy.  Try feeding him a cooked frozen pea.  Remove the outer layer, cut it into tiny pieces, and feed the pieces to your Betta one at a time, making sure he eats it, and that it does not fall to the bottom of the tank.  A betta should have one pea a week, and on the day you feed him the pea, feed him nothing else.  This is so he can clean out his system.  He should also have Daphnia in his diet.  When feeding a Betta, he should have 2-3 small meals a day, and not one big meal.  Example: 2 pellets for one meal or 2 flakes for one meal.  We must always remember that the Betta's tummy is the size of his eye when feeding them.
I would also like to mention that heating a betta's water with a light is not good for them.  Bettas prefer the light of day.  They should have a thermostat, and their water should always be 80-82 degrees.  Under this temperature the betta is cold, and will get sick.  Heating with lights also causes the temperature to fluctuate, and this is very bad for the betta, and any other fish.  
Vendors do not give good information on Bettas.  Bettas should be in heated 5 gallon tanks, or bigger.  In their habitat the water may be shallow, but they have lots of room to swim.  When heating a tank for a betta, this must be done very very slowly.  Raise the temperature one degree every two days, as bringing up the temperature to quickly could cause death.

The Betta is one of the most mistreated fish on the market.  This is not your fault, but fault on the vendor who does not care.  They are there to sell their gadgets, make money, and couldn't care less about the Betta.  When they say that bettas can live in small containers, this is untrue.  They may live, but their lives are cut short.  Eventually they get sick, and little can be done when they are in such small tanks.  He is an intelligent little fish, and should be treated right.  
I would also like to mention, that a 1.5 gallon tank does not need a filter.  It is better to change his water every 4-5 days.  
For now make sure that he has no ammonia, or nitrites in his water.  Ammonia is the number one killer of fish.  Feed him the pea, and see if he feels better in one day.  If not, you will have to treat him with Tetracycline, or Furan-2.  Do a complete water change before medicating, using a good water conditioner such as "Stress Coat" or "AquaPlus"
I hope the little guy feels better soon.
Lynda