I have a red betta, he is beautiful and about 3 inches long, head to tail. I decided to get a bigger tank for him, 10 gallons. I didn't want the tank to be empty so I also perchanced a small Pleco and 5 tetra. I let them be in the new tank for 24 hours before I added Buddy, he didn't like sharing a tank and over night killed 4 of the five tetra and was harassing the Pleco, he had to be moved back into the 3 gallon tank. Ever sense then he seems to be very upset. I had moved another much smaller betta into his old tank and switched them after the clearly not working tankmate attempt. I did do a good cleaning of his old tank, but not right after the switch, it was kind of an emergency to get him out of there, i didn't realize how bad the water was at first, for about one night. Once i did I took him out and cleaned his tank very well, scrubbed everything and replaced the filter. NOw sadly though he is laying on the bottom of the tank, up-right, eating vary little, and not making a bubble nest which is very unlike him. I trained him to jump for his food, and normally his morning feeding is the most exciting but he simply looked at my fingers holding the food, got ready to jump and changed his mind, he would rather of not ate then jumped for the food it seemed. I'm really worried I put him under too much stress. There are no physical changes i can see, i got a water treatment just in case and used that a few times after the mishabe with the other fish. Do you know what I could do for him, or anything to make him his old self. I feel so bad but there isn't anything I can do for a while. i could get him a bigger tank but not for a month or two after a few paychecks, i spent a lot on the new one I have now. both tanks have heaters, temp gages, and filters and they stay between 72-78F. I have had him since Christmas 2012 and i don't want him to die. His long tails have been curling at the ends too, but not his swimming fins, i'm not sure if that means anything, he grew a lot once i brought him home from the store and his color is fantastic.
First thing I would do is test the water for Ammonia, nitrites & nitrates. From the description of how thoroughly you cleaned the tank I'd say you are now going through a fish in cycle. If you don't have a liquid test kit on hand do a water change of 40-50% to see if that makes any difference. I would also get the temp more stable of 78-80F.
I did a 50% water change. I noticed that he had small white specks on him and was like "NO ICK" I already had some water treatment handy and used that right away when i noticed him getting sick in the first place. I after taking 50% of the water out put buddy in a separate container in the tank and tried hot water treatment and got the temp up to 86 degrees F. while the hot water in the tank would kill the ick, and then would gradually get the water in his tank to the same temp. after I let the two become the same temp I let him back into his tank and he swam a little but then went to the Styrofoam cup i cut in have for him for his bubble next, he stayed next to that and kind of had it hold him up close to the surface. I continued using the drops two times a day as recommended if the case was bad enough. for a week and a half he was swimming with more of a jump then a flow of movement, and it seemed his fins were getting stuck, but today he is great! best he has been, he actually fought his reflection, jumped for food, asked for food three times, i gave very small amounts he hasn't eaten in a few days and i didn't want to over feed him. i will be ecstatic if he has a bubble nest by tomorrow morning because then i'll know for sure he is doing better. Thank you so much for the reply! It helped a lot!
I found out too the hard way that Bettas really don't generally do well with tank mates. Many, many years ago, based on the advice of the pet store worker, I bought a Betta and some tetras. My Betta was so aggressive towards them, that they huddled in one corner. The female tetras became aggressive towards the male tetras and ate them alive!!! Not a pretty sight to see a fish swimming around with one eye, no tail, blood pouring out of its side!!
Oh, and one more thing, bubble nests are not necessarily a sign of health. I learned that one a long time ago as well from my best friend's sister who kept her Betta in a 4 oz cup, and hardly ever changed the water. The water was so dirty you could hardly tell there was a fish in there, yet, there was a bubble nest so large it was overflowing the top of the cup. On the rare occasion that she did change the water, he would immediately rebuild the nest to overflowing. Needless to say, he only lived a few months in those conditions.
For buddy a bubble nest means the water is just right and that he is feeling good. Im going to do a 20% water change to get some of the chemicals i used out, and see if i can level out the tank, the medication he is on make everything a little off for him. My crowntail did awesome with the tetra, they actually fallowed him around. :)
Tetras need at least 6 to feel secure and happy so if you don't rehome the remaining one, then you need to at least up the schoal to 6. The pleco if it is a smaller type like a BN needs at least a 20 gallon and if you happened to get a common pleco...that sucker will easily get at least a foot long with a possibility of 2ft so it will need a pond or a huge tank (300 gal).
Some bettas will tolerate other fish and some will tolerate NOTHING in their space and that includes snails. LOL All depends on the particular betta in my experience.