betta not eating moved to larger tank

Question
I moved our betta, we've had him for 9 months, from a small tank to a 3
gallon tank. Put in a small and tall live plant and two swim through
structures. He had one of these and a plastic plant in his small betta tank. I
did this Sunday. It is now Wednesday and he seems not to eat. I have feed him
bloodworms, I now see he needs variety but that is all he will eat. He swims
around the tank freely and appears fine but doesn't eat, he was really excited
swimming and riding the wave for a few days but has calmed down. I
replaced 1/4 of his water. Do you have any thoughts on why he's not eating
and what I should do. I will try the frozen peas tomorrow once I get some.

Answer
Hi Melinda,
Check your water to make sure there is no ammonia, or nitrates in his water.  If you do have ammonia, change all the water using a good water conditioner such as Stress Coat or AquaPlus.  Is his water cold?  The betta is a tropical fish, and needs warm water.  He should be in 78-80 degree water.  If you do heat his water with a heater, do this very very slowly.  1 (one) degree every two days, as warming his water too quickly would cause death.  A cold Betta will not eat, and gets sick.  Whenever a Betta stops eating, there is something wrong...we must try to find the answer.  Check him well to make sure he has no spots, or discoloration, anything that would tell us what is wrong.  His food could be outdated.  Is his tummy swollen?  His tummy is located just under his chin.  If his tummy is swollen, you could try the pea, but if he does not eat the pea, you will have to treat him with antibiotics.  If he is constipated, it will lead to Swim Bladder Disease.  "Kanamycin" is very good for swim bladder, but sometimes hard to find.  If you cannot find it, buy "Tetracycline" or "Furan 2"
It's a wild guess, but could the live plant have something to do with this?  It might be taking up lots of oxygen in the water, or too much room.  I'm not a plant expert, so not sure about the plant.
Check all of these, and hopefully we will find out what is wrong with your betta.
Lynda