please help my fish

dr heckle

hi my 2 yr old siamese fighter neptune has suddenly began acting extremely wierd he isent eating his coulors have faded he dosent move unless its to to breath from the surface he is having trouble swimming and when he is sitting unless there is somthing he can lean on he merely rolls over onto his side and has trouble getting back up again.
he lives in a 20 liter tank that is kept to a constant temp of 24 degrees.
in his tank he has a large java fern and a medium size ceramic log.
his tank has a filter but since he got sick i have turned it off as per the instructions on the back of the bottle of melafix that i have been treating him with.
i have also been doing 25% water changes every 2 days since all this began.
this has been going on for nearly a week now a nd he appears to steadily getting worse at first i thought it might be just stress as i recently had to replace the heater in his tank (the new one was exactly the same as the old and i have been heating the tank to the same temp that i always have.
another sympton thats probably worth mentioning is that fact he is losing wieght FAST!!!!!!!.
please help my fish ive run out of things to try

Lupin

What are your water parameters at this time? What filtration were you using? Unless it has activated carbon, there is no need for you to turn it off. For a betta tank, I'd simply stick with either sponge filter or no filtration but compensated with plenty of water changes though I prefer the former.
Have you observe the appearance of his poo? You can use levamisole hydrochloride if the poo is whitish and stringy. Considering it is safe, I'd dose 2 mg per liter. Do make sure the water parameters are on safe levels.

dr heckle

hi its an active carbon filter and he hasant produced any feaces since he got sick :(

dr heckle

hi its an active carbon filter and he hasant produced any feaces since he got sick :(

Lupin

Switch to a filter that will allow space for filter floss. All you need for filtration is sponge or filter floss. The activated carbon itself does not last long and is best used up to 4 weeks only. Replace it afterwards but I find it, in my opinion, a waste of time and money considering you have only one betta and there aren't even any contaminants I believe that would enter your tank if you are careful about it. If I might make a suggestion, store a new pack of carbon in your cabinet until needed.

It seems your fish must be starving to death. Raise the temperature to 84 degrees Fahrenheit and dose with metronidazole. This will help stimulate his appetite.