What's the temperature like in your tank? Usually an otherwise healthy betta lying on the tank bottom all the time is a result of lower than preferred temps, although healthy ones will rest between bouts of activity.

This behavior can also occur when the fish is weak from illness, does he have any other symptoms? Look at him real close and see if there is anything unusual.

What's the decor like? Sometimes a behavior like this happens when the betta isn't comfortable. In my experience bettas are the most active when kept in a planted tank, with lots of places to explore and rest and hide. It will appreciate minimal surface disturbunce and some floating plants if possible.

the temp is almost 80F. It's a 20 gallon tank with fake plants. There is also a number of large rocks that provide hiding places but he stays away from them and sits in the corner. I think i will pick up a few more plants the next time I'm out though. I've been watching him really closely since I noticed that he wasn't moving a lot but everything seems the same. No color changes, no unusual spots, though he has begun to keep his fins really close to his body. He was acting like this in his old tank and I assumed it was the tank being too small and the fact that I didn't have a heater, which was why I switched him over.... and he was fine, happy and perky at first but he's back to this...

HI ArianaPerry, It sounds to me like you have done all the right things. I know! maybe give him a treat of live worms or brine shrimp. See if that will perk him up if he is just moody. Tonight I found my perky Betta laying on the bottom which is not like him, but as soon as I came up close to the glass, he moved quickly up the surface. Maybe he is being effected by the water tempature change from no heater to heater. I have read they like warm water but maybe he didn't adjust to it or the quick change weaken him. I really don't know, I am grabbing at thoughts.
I wish I could help you.
Theresa

How long has he been in the new tank? Sometimes they sulk while they adjust to new surroundings. Is there a strong current in the tank or a lot of surface disturbance from a bio wheel or bubblers or whatnot?

he's been in the new tank for about three weeks now. I'll try turning down the filter which does cause a lot of surface disturbance and I'll pick up a treat for him. Thanks for all the help.

I'll bet he has something else wrong with him IF the reduction in water turbulence doesn't do anything to improve him. If you change your water pretty regularly it sounds like betta heaven to me. So see if you can find some Pepso food to feed the whole tank for a week. For some reason even somewhat sick fish seem to love it, and I feel that most fish eat better and more when they're in a mildly competitive feeding situation. That includes discus and bettas.

just a heads up... My betta has purked right up since I turned up the heat in the tank and turned the filter down. I've had a few problems with my other fish. One died with no warning at all. He was fine one day and not the next. But I guess you never know what you are getting when you buy them. I only had him for about two weeks. And another fish got stuck in the filter and died. I miss them. Oh well... back to the fish store for me. Cheers