... the brown algae is probably diatom, and is usually a part of the cycle process. It will go away in time if you keep your water parameters in check.
You really should take a sample of your water (at least a pint) to the LFS
and ask them to do a thorough test battery. They will be able to tell you where you are at in your initial cycle, as well as any problem areas you need to address. You will run into all kinds of problems if you don't know what exactly is in your water. Most reputable LFS
will test your water for a few dollars. If you prefer, and it is probably more economical to do this, go buy a good saltwater test kit. Salifert makes a good kit that isn't terribly expensive. You will definitely need to learn to monitor your water at a minimum of once a month, and more likely every two weeks with a system that small. The smaller the tank, the less room for error you have.
I agree with everyone above about the Fenner book and needing a QT
tank unless you are going to add all the fish and/or inverts to the tank at the same time and they are all from the same source. That isn't a good idea, BTW
, so get the QT
tank. You will regret it if you don't.