The tank has to cycle still. Waste produced by fish, decomposing food, and anything else not alive (dead pods ect..) produces ammonia. This is toxic. The ammonia get converted to Nitrite by beneficial bacteria that grow in your filter, in your substrate, and on your liverock. However, the nitrite is also toxic (but not as toxic as straight up ammonia). Next the Nitrite gets converted to Nitrate by more beneficial bacteria. Nitrate is not nearly as toxic as the previous two substances, but can still be a problem in a tank. Algae such as coraline, diatoms, and hard green algae will grow and use the nitrates in your tank as food. Once your tank is fully cycled you'll just have trace amounts of Nitrate left, and very low or zero ammonia and nitrite.
Because of the high water volume of your tank compared to the number and probable size of your fish, you'll probably be ok for a few days to a couple of weeks (depending on how much you've been feeding them), but I would suggest getting ready to do some PWC (partial water chages) to get your toxic elements down. To do this, buy RO/DI water from your LFS, or if you have the extra funding buy one. Its officially a Reverse Osmosis/ De Ionized Water unit. You can buy the water with or without salt, and if you have the unit you'll have to mix your own. This also means the purchase of a hydrometer or refractomete....it adds up quickly. Anyways! Make sure the tempter and salinity of the water is good, siphon out some old and pump/pour in the new!
Small side note: you don't want to use tap water. Its possible in an emergency, but if you've got city water like me you'll be adding lots of additives like Florine and maybe iodine or other strange things the government puts in the water to make me stupid. You don't want stupid fish with shiny teeth, so better to stick to that RO water.
While cycling the tank you'll probably need to do a few of these, and depending on your proximity to the LFS, it might be a good idea just to buy the RO unit. Water from a lfs runs me about $20 for 14g, and thats about a 10% water change for you. If the levels get toxic enough you'll need to do higher percentage water changes to keep your fish healthy. What are the levels exactly? It doesn't take much to crash an early tank.
