Where do you buy co2 tanks at?
Do you get them filled at the same place? how much?
Is it safe to buy one online and have it shipped to you?
2.5lb or 5lb for a 10 gallon tank?
This is my first planted aquarium and i'm going high tech, so I have lots of questions as I go!
If you live in a larger market city, check craigslist. You may find a good deal. Other than that you can usually get a co2 cylinder from a welding supply or fire protection company. Also homebrew places will have access to co2. All three of those places will either fill or exchange your tank or will at least be able to point you in the right direction.
If you plan to buy online, aquariumplants.com is a good bet. As is Amazon and eBay.