Since yesterday my fish has stopped swimming around his tank. He just floats at the top not doing anything. His appetite is fine, and he shows no other symptoms of being sick. What could be wrong with him? Please help.

How old is he?
How long have you had him?
What are the tank conditions, mainly ammonia?

Most likely you need a water change.

Could also be due to constipation or over feeding. Try boiling some spinach, peas or zuccini and dice it very fine and feed him very little. The fiber should clean him out. Make sure to remove any uneaten food.

I've had him for about 6 months. The conditions in his tank are as follows:
pH- 7.2
gH- 9
Ammonia- 0
Temp- 76*

He just had half of his water changed yesterday, per the usual schedule.
He eats 3 soaked pellets twice a day.
I will try giving him a pea and see if that makes him feel better.

Pop the pea open and just give him the inside.

The fact that you did a water change yesterday is concerning. Normally when things go wrong you look at what has changed recently. Is it possible the the water you used or the container it was transported in was contaminated? You may want to run some activated carbon through the filter just in case. It's pretty good at removing chemicals.

did you condition the water and remove clorines?

although the symptoms sound more like swim bladder or caused by constipation.

a peeled, thawed frozen pea, cut into tiny bits and soaked in garlic juice should help if its that.

good luck, keep us posted on your beautiful boy!

__________________
Yes...I kiss my Betta Tanks!!

False alarm everyone!!!
When I changed his water yesterday I took one of his plants out and forgot to put it back in. Today when I put the plant back into the tank, he started swimming around like he was the happiest fish in the world. I guess he was just sad without his favorite plant, lol !!!

Glad to hear Candace! Don't do that again, lol!

LOL never get worry if your bettas are sticking to the top and the tank is empty...although if there is problem...i wouldn't suggest using any veggie as it isn't their natural food source. they are carnivores not omnivores, if stuff did happen...use frozen blood worm or live, mosquito larvae will do also. they contains high nutrition and that may be what your fish is lacked out of, feeding only pellets...i wouldn't recommend any brand besides atison pro, other wise...go frozen or live for best result.

We generally use the vegetable material as a laxative not as a meal and it works. I have seen many bettas saved by this method. I recommend it but not as a meal replacement unless they are not eating anyway and are in severe distress and then I have been known to recommend it be given for a period of a couple days to clean them out. Overfeeding may constipate them and 76 degrees is a bit cool for their metabolism. The digestion will be a bit slower and constipation could have been the cause. I am so glad it was just the little pout for the want of the favorite plant. They do get very attached to their favorite items.
Wild bettas may not be so finicky but pet bettas do get very spoiled and decide very quickly that they like what they like and want what they want when they want it. They also have a tendency to become depressed if not humored. People call me silly but I am with my fish 24/7 and can watch their behavior and notions very closely. It is obvious if you spend time with them and make over them that they have definite personalities and they know what they want.