not eating

I have had my betta for a few months now and over the past 1 or 2 days he has just sat on the bottom of the tank and hasn't eaten, when i go to see if hes alive (by brushing water around him) he darts around very quickly and returns to the same spot on the ground. I looked online and did the...

I got a 38 gallon tank to put my rainbow shark in...he was in a 10 gallon with other fish originally and someone told me that is a big no-no. So he is the only fish in my 38 gallon tank. I have had him for a few days and he likes sitting behind my quietflow filter for pretty much all hours of...