Also, Prime will not help the cycle along. The cycle is a process in which beneficial bacteria colonize the tank. Prime does not do anything to help add bacteria to the tank or help them multiply any faster. It merely treats the water so it is suitable for aquatic life (removes chlorine and chloramines from the tap water).
What the fish guy may have been trying to suggest is that Prime will help fish survive in a tank that's not yet cycled. While that is true, it's not recommended. It is only done when a person has inadvertently put fish in an uncycled tank and has no other way of keeping the fish alive (but there are no guarantees as you have to double, triple dose the Prime).
It is, however, a great way to cost the customer more money. They buy lots more Prime than they would normally need. They add fish much earlier than is safe. When the fish start dying, they then sell the customer medicines to try to cure the fish. And when the fish die, then can then sell the customer even more fish. So they sell more Prime, sell meds, and sell extra fish. It's a great way to sell more stuff. However, it's not recommended for the fish or for the person starting out with a fish tank.
Cycling a tank can take around 6 weeks (give or tank a few weeks). So you can see just how much Prime you'd be adding to get fish through this process.
Algae in the tank indicates too much light. Either reduce the amount of light being used, lift the lights up so they are further away from the tank, and/or don't run the lights as long. It's best to start off with low lighting at this stage of things. Whatever you do, do not buy an oto to eat the algae. While they're great algae eating fish, they have a high mortality rate when first bought and are definitely not a good fish for an uncycled tank. Also stay away from common Plecos. They do not eat algae as commonly suggested, poop like crazy, and grow to a huge size (you'll need both arms to hold it once full grown). They grow fast so don't let someone tell you that you can enjoy it while it's little. It won't be little for long. There are other Plecos that are appropriate, but they should not be put in the tank until after it's cycled.
The first thing you need to do is read up on cycling a new tank and buy a test kit. The API Freshwater Master Test Kit is the one most recommended. It's much cheaper from Amazon: http://www.amazon.com/API-FRESHWATER...aster+test+kit
. This will allow you to check the water conditions while the tank is cycling so you'll know when it's safe to put fish in the tank.