Not sure if you read this thread but great info to be had;
What water are you going to get from petco?If it is not RO/DI or distilled don't waste your money.I do think reef tanks need water better than most all of us get from our taps,but "spring/bottled....." water is no better IMO.Walmart will have distilled for $.89 a gallon,or most good LFS(not petco or petsmarts) will sell RO/DI.
As far as your light it is one of the most important thingss for a reef.Needs to be 10,000-20,000K in tempature.Incorrect lighting in marine aquaria is an invitation for algaes that have lived for thousands/millions of years and often are all that is needed to turn a decent tank into a cyano factory.
Being only 10g you don't need a protien skimmer,but for most reef tanks they are very important also.For the most part any tank under 30G can be sustained with proper waterchanges.When you get sick of waterchanges a GOOD protien skimmer is one of the most important pieces of equipment also.Always get one rated for AT LEAST 2x the tank volume.
You will need to do regular water changes PROBLY unless you get into carbon dosing or bio plastics.
Marine tanks are far less tolerant of elavated nitrAtes and all sorts of issues can arise from things that don't cause as much trouble in freshwater
,like phosphates,copper,and other things that are not as critical in FW.
A good test kit will be needed as you have to keep an eye on ;DKH(carbonate hardness),pH,calcium,magnesium and eventually other traces.
Read Reefing Madness thread as it has great info and links,and check his signature;THOSE ARE THE LEVELS YOU STRIVE FOR!