Thanks! Also, I have no idea what type of filtration system I need for a saltwater tank, I have a 10 gallon freshwater tank. Should I get a canister or hanging filter? If it was a freshwater tank I would get a 50 aqueon filter but would one of these remove the salt from the water? Also a man at a local fish store told me he sells his tank water and it has been cycling for years. He also said not to change it and if I did only do a 1/10 change, is this right? Will you or anyone please also list all the technological (filter, skimmer, heater, etc,) aspects I will need for this tank and their wattage/power needed.
For a tank under 40g, a skimmer isn't a necessity. They're nice to have, but if you're good about weekly PWCs, that should be enough to keep params in check in a tank that small. I don't have one on my 30g, and have no algae at all.
If this is a FOWLR tank, any light you have will work, it's all a matter of what you like. The fish don't need a light, it's for your viewing. If this is going to be reef, then you'll need a good light, like T5 HO or LEDs. I've heard good things about taotronics LEDs on amazon, so check then out. For that size tank, you would need 1 of the taotronics.
Or filtration, there are several choices. You can do a canister or hob. Just get something rated for at least twice the size of your tank. In my FOWLR I have an AC 70 an AC 30, on my tee I have a Fluval 406. If you get either I these, you'll need to clean them out and rinse all media in tank water every week to prevent nitrate build up. Or there's the Berlin method of filtration, which uses only LR and an overpowered skimmer. Then there's a sump, too.
As for buying the water, my understanding of what you wrote is that a SW store customer was offering to sell you water- is that right? Wasn't sure if you meant another customer offered it or the lfs employee was offering. Don't buy water from a random guy. THere's very little BB in the actual water, it's mostly on surfaces like sand, rock, and filter surfaces, and you could be introducing bad things from their tank into your tank. You should use RO or RODI water for SW, though. If you don't have a RODI unit, a lot of SW fish stores will sell water by the gallon. You just gotta haul it back home. :/
Have fun planning your new tank!!