Sick Betta! Help :(

Question
I love my little betta Nappy and I was trying to be a good mother and get him a little house to sleep in so he wouldn't be bothered by the lights, and I think I poisoned him. I know I should have gotten him a fish house, but all the ones I found weren't the right size for him. So I found something that looked like stone (marble) so I thought it would be ok to put in water, I washed it, put it in his cage on Sunday. Last night (Monday) he was lethargic and this morning(Tuesday) he wasn't moving or eating. I immediately took out the little house and it smelled like chemicals, so it was obviously making him sick. I put him in a new bowl with completely fresh water, but he looks bad. I didn't think he would make it through the day, but he's still alive. He stays pretty still, looks pale, won't eat, and tries to stay near the top but gets too tired or something and just sits at the bottom. He was a very healthy fish before. Is there anything I can do for him? I don't want to see him suffer, but I also hope he can pull through this. I'm just scared that fish are so little that when they get sick thats sort of it for them :(
Thanks so much for your help

Answer
Eva,                                                         Don't put the house back in there. I don't know what to tell you... I would just keep an eye on him. I would put some aquarium salt in there it is like a laxative for him and try to clean his system out. 1 tbsp per5 gal. Keep changing the water as necessary , but not too much to upset him.   Please let me know how he does..,tina