ok my girlfriend has had this fish for i donno hoe long its been a little while. But ok it lives in alittle bowl not too little but not very large and she cleans it about once a week but within 2 hours of it being cleaned its water is nasty and after a week this fish creates an ungodly smell i literally gagged when i got within three feet of the bowl and my question is what is causing this because she has 4 other betta fish in the house and none create this god awful smell, and 2 of the others are in the same size bowl. so what could be causing this and is there anyway to fix it?