betta behavioror

Question
hi i bought my betta fish today and the pet store gave me the fish in a small cup type thing and they put a tablet in it that turned the water blue, the employee told me that it was a stress tab. when i got home i put him in an aqarium with colorful rocks, a castle with too openings and a fake plant. for the first hour he stayed by the bottom then i fed him some bettamin, tropical medley and he came up to eat and swam around alittle, now he is hideing in the castle and has been in there for a while. is he ok? do i have him in too big of a aqarium too quick? ( its about a gallon) i think.  i used sink water and didnt let it sit for 24 hours because i just learned that. im not sure of the temp but it feels fine... should i turn on a light? please help with any info you can give  thankyou and sorry for all the questions, thanks

Answer
Liz,
You need to ALWAYS use tap water dechlorinater or conditioner! Tap water has Chlorine and Chloramines in it, and it it very toxic to your fish - it will burn their gills until they die. You should go back to the store ASAP and buy it.
Make sure it says "Removes chlorine AND chloramine" on the label.
Simply letting the water sit out for 24 hours does not work, because while it does allow chlorine to dissipate, chloramine takes several weeks to dissipate, and is even more harmful to your fish.
Secondly, your fish just went for a car ride, and was put into a new home without any kind of stress reducer, so he is a little freaked out right now.
It will take him a few days to adjust to his new home, just like any other animal on Earth.
There's no such thing as "too big of a tank." The bigger the better.
And less than one gallon is not much, I always recommend at least two gallons.
Make sure you are completely changing out his water once a week, never use soap, just warm water to rinse of bowl and gravel, and always use tap water conditioner before adding him to the new water.
AS for light, the majority of freshwater fish are going to need a natural day/night cycle just like us. So yes, you can put on a light for him. I recommend buying a small thermometer so you can keep an eye on his temperature. They are tropical fish and should be kept between 75-85 degrees F.
That's about all for now, you can type "Betta Care" into any search engine and find a site on exactly that if you have any other questions.
DON'T FORGET - he needs tap water conditioner NOW!
You should also get stress coat or aquarium salt and add a small amount to help reduce stress.
Stress lowers immune system and kills fish!