betta fish dying?

Question
my fish has turned sort of black and white fuzzy stuff looks like it's growing. it's not moving a lot. sometimes it's floating on the top and sometimes on the bottom. it floats on it side and the fins hardly move. when i take him out he moves a little after out of his bowl but then just lies. i have token good care of it except i didn't change his water for like 3-4 weeks. is it dying? thank you for your help!

Answer
Hello,
You must run, not walk to the pet store, and get him medication right away.  I hope I am not too late.  He has fungus due to poor water conditions, and if left untreated, this disease will eat at him until he dies.  Fungus is a rapidly growing disease.
Change all of your water using a good water conditioner.
Treat him with Maracyn, and Maracyn 2 combined or "Tetracycline"  Follow the directions on the package, be careful not to overdose.
Bettas should have their water changed every week without fail, and sometimes twice a week depending on their living space.  This is so important.  If you do not do this, ammonia sets in, and this is deadly to fish.  They are living in their waste, and spoiled food if left without water changes, and get very very sick.
I hope you will save the little fellow, and if you have anymore questions, do not hesitate to write me, but for now you must act quickly.
Lynda