Lethargic Betta

Question
I bought a crowntail Betta almost two weeks ago.  He is in a 2.5 gallon tank with gentle filtration, a heater (which keeps the water at a constant 78%), and an overhead light.  I turn the overhead light off at night to let him get some rest.  He also has some live plants in there with him, all of which appear to be healthy and have no rotting leaves.  Within the last 48 hours I've noticed that my Betta has become very lethargic (although he is still eating normally).  He sits at the bottom of the tank for long periods of time (5 minutes or so).  He will swim around for a little while, but quickly goes back down to the bottom to rest.  I researched the behavior and became worried about ammonia levels in the tank.  I did a 50% water change and added drops to neutralize chlorine and create a protective slime.  However, my Betta is still acting lethargic.  Is this normal?  If not, what else can I do?

Answer
Jenna,

 They only way to know if it is ammonia is to test the water. If you don't have a testing kit, it is a good idea to get one. Do not buy the test trips because they are not accurate. The drops you added have to be put in the new water before adding it to the tank every time. I would gradually turn the heater up to at least 80 degrees. They like their water warm. Adding the drops to neutralize chlorine is not the same as taking care of the ammonia. I would also remove the filter. Betta's do not like any current in their water. Are you sure your water temp is 78 degrees? Do you have a thermometer in the water or on the tank glass? I have a feeling the heater is not keeping the water warm and even at 78 degrees he should be more active. If you are using a heater that says it keeps the water a certain temp, then that is the problem. Those kinds of heaters don't work as well as the ones that have a dial. I am thinking that when you get the water warmer, he will become more active.