Quick decision needs to be made

[Fin Fancier]

Yesterday I got a female betta from petsmart, brought her home and after an hour of acclimating released her into my 5 gallon tank, water was 76 degrees, had a heater, so no heat shock, and was conditioned. A test strip showed nothing wrong with the water, but by this afternoon she was dead. (employee said it might have just been weakened by shipping).
I went back to the store and had them double check the water, the strips showed nothing, so I rinsed out the tank, conditioned the water which is 78 degrees and let my new guy go after an hour of acclimating.
The problem is he seems lethargic after about an hour, just sitting at the top, much like my female did last night, so I've got him floating in his cup from the store (in his original water) at the top of the tank. The petstore is less than a mile from my house so I can't imagine the water is drastically different, but I don't want to wake up in the morning and find him dead. Suggestions?
Should I go out and buy bottled water?

I had another betta a couple months ago. She lived for two weeks with no problems in water that I had not treated but had left to sit out for a week. She died after an untreated water change that I only let age for 2 days. Fish can live in this water, so I'm starting to wonder if its the lack of aging or the tank. I did get it off of craig's list, but I let it soak in hot water several times. I can't figure out what's wrong.

[MyRainbowBettaFish]

is your tank cycled?!?!?!?

[Fin Fancier]

No. It's a new set up, 5 gallons. It's had a fish in it for approximately 2 hours. Am I overreacting? I'm just worried. He was so active in the cup and then he just sat at the top lethargic after a half hour. The female faded fast. I'm worried the same is happening to him.

[babystarz]

I'd say wash the tank with bleach, then rinse it 20+ times, then leave it outside in a sunny spot in the morning and keep it there until it's dark. The sun will remove any traces of bleach.

Also try getting your next fish from a different store, because those fish could have been sick before you brought them home.

Before switching to bottled water, ask your utilities company for a tap water report. This will let you know if there's anything elevated in your water that could be causing problems.

Edit: Just realized you're from MN. Which Petsmart did you get your fish from?

[Fin Fancier]

The petsmart in St. Louis park.

They've been doing construction on the roads, but we haven't had any construction notices about the water. I don't think he was sick at the store because he was really active in the cup then not so active in the tank. I'm wondering if I should just leave him in the cup for the night... But if I leave him in the cup then I'm worried about him getting ammonia poisoning while I tear down and treat the tank. Hence the question about maybe bottled water, and if that's the case what kind should I get (not brand, I just can't remember if it's spring water, or a different type you're supposed to buy).

[Hallyx]

Really good advice from babystarz. Can you get a large Tupperware container to keep him in while you sterilize his tank? Leaving him for a day in a cup of freshly-changed/conditioned water is fine.

Spring water (not distilled) is an option not often recommended around here unless the tapwater is absolutely deadly and undrinkable.

What brand conditioner are you using?

[babystarz]

Originally Posted by Fin Fancier

The petsmart in St. Louis park.

Ah ok, haven't been to that one. I was just asking in case it was one I know to be really bad at betta care.

I am skeptical that your water is the problem but if you want to buy bottled go with spring water. Overly filtered water lacks minerals that are essential to fish health.

[Fin Fancier]

I think my problem was the conditioner. I went back to petsmart this morning and bought amquel plus, I was using aqueon betta bowl plus last time. I switched him to a 1 gallon I had and conditioned the water with amquel, he seems much more active than he did last night. I think he'll be fine in there until I sanitize his 5 gallon, I bought some diluted bleach on the way home from the store, now to figure out what 1/20th of 5 gallons is. I think we can safely welcome Gills O'Reilly to the family now.

[babystarz]

Glad to hear it! I didn't even think to ask what conditioner you were using.

[OrangeAugust]

also get a liquid test kit. the strips are unreliable.