My Betta fish is lying on the bottom of the tank on his side, and doing very little.

Question
I bought a betta fish about three months ago and I keep him in a baby BiOrb (15 litres) in my bedroom. It is heated to about 26 degrees C and that temperature remains constant. In the tank with him were two black phantom tetras, and three cherry barbs. A week ago I had to quarantine my betta in a breeding tank which was placed in my biOrb because the cherry barbs were biting his fins. They didn't manage to chew too much of his fins as they are still very long (they chewed about 2-3mm off his tail fins#. I quarantined him for two days and he started to become very pale and he was loosing his bright turquoise colour so I switched the cherry barbs and the betta around to the barbs were quarantined instead and they have been for the last 4 days. Yesterday I treated my BiOrb with a 'first aid kit' #which is a replacement filter specifically for the biOrb and a treatment pack you put in the tank# however when I got home today I found my betta on the bottom of the tank just lying there, his two fan like fins on either side of his body werent moving and the only reason I knwe he was alive was because his gills were moving and he would dart around if you hit the side of the tank. I also found one of my phantom tetras dead and covered in fluffy white suff dead at the bottom of my tank wedged inbetween stones. I took him out and carried out a 30% water change upon instruction from the fish shop and i treated this water to de-chlorinate it. All my cherry barbs are fine in quarantine and look very healthy but I am very concerned about my betta fish, as I have to say he is probably my favourite, and he is the fish I based the selection of his tankmates upon. I will soon be removing the cherry barbs from the tank completely and buying a new tank for them, but my betta isnt doing very well.

I haven't carried out any checks on my water quality yet, and will take a sample to the aquatics store in my town tomorrow. I feed my betta the same as my other fish #flaked fish food# and until yesterday he has been fine eating it. Please help!!! I love him to pieces :#

Answer
Jessica,

 First off I would raise the temp to 28 C. They need to be in warmer water. That would make them in 82 degrees F. I think he is stressed out from the treatment he has been getting from the Barbs. I think it's a great idea that you will be moving them and I would do that ASAP. As a rule of fin, never treat the tank unless you see illness ie: Ich, clamped fins or fin rot. Velvet etc. While you are getting the water checked look for a Betta hammock. That can be placed towards the top of the tank. He will then lay on it and not have to work very hard to get air. It is also a good idea to have your own water testing kit. Always check their water for PH, Nitrites, Nitrates,and Ammonia. Poor water quality is the number one reason behind illnesses. I do believe that once the other fish are removed from the tank, and once the heat has been raised a bit, he will start to get better. If after 5 days he is the same or worse let me know. It is always a good idea to change their food around. I have 11 adults and they get frozen and freeze dried blood worms and brine shrimp, pellets and flakes and since I always have fry(babies) they get an occasional newly hatched brine shrimp. Also, pick one day a week to fast your Betta. Make sure its the same day every week. This helps to digest the food in their tiny tummies and will help keep swim bladder disease at bay. Please, if you have any other question don't hesitate to ask, that's what I am here for.