After cleaning my gravel and changing a part of the water, the new water became very cloudy. What happened and what advice should I take? I have 3 serpae tetra, 1 painted skirt tetra, and a tiger barb.

to the forum you will find many many knowlegable people here who are more than happy to answer or try to help with any questions you have, there is no such thing as a stupid or dumb questions (Apart from the nes you dont ask)
with regards to the cloudy water....
are you able to list the dimentions of your tank andy what type of filtration you have (U/G, internal filter or external filter) also Sas the tank cycled
if not a good place to start from to get the basics is [post="0"]
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/www.fishforums.net/content/Tropical...-Tank-Syndrome/[/post][/URL]
How long have you had the tank set up ?? has it recently been set up or is it a mature tank (running for 6+ Months)
have you been able to take water stats ?? (Ammonia, Nitrite & Nitrates)

if so can you post them so we can take a look, there is a chance you may be going through a bacteria bloom if the tank hasnt fully cycled yet, If you dont have a test kit it is well worth getting one !!! they are worth their weight in gold.
if your in the uk your looking at about £18 for a good quality liquid kit like API, Try to stay away from the dip strips there not worth the plastic theyre printed on.
again Welcome to the forum and remember dont be afraid to ask any questions
Scott