Alk is at 4meq/L? If so that is ok. Normal alk should be between 3-4 meq/L or 8-12 dkh, and your PH should be 8.3. Raising your alk will also help raise your PH, and since it is at 4, try and raise it but use the dkH reading for now and make sure not to pass 12....... CA should be between 400-480. If you dose for alk and ca, use B-IONIC, or homemade 2 part and strive to keep those levels in their respective ranges. BIONIC is the BEST bang for your buck, and is the most widely used 2 part product that is not home made. KEEP A LOG OF YOUR LEVELS! Keeping a log is extremely beneficial to understanding how much CA and Alk is being used by your tank, and it's inhabitants. Once you figure out those amounts, you can adjust your dosing regimen to keep them perfect all the time. That tends to be the hardest thing for people to do.

The brown is from diatomatic algae, which is a normal part of the tank's cycle. You can add some hermits and snails now, they will help keep your tank clean, and are necessary to help eat excess foods that would normally go uneaten. At some point copepods will take off, and they eat poop. Don't buy a mandarin or scooter blenny because they will eat your pods. If you still want a mandarin after about a year, then get one. After that time your tank should have enough copepods to support them.

Oh, and just about everyone goes coral. So buy your lights accordingly!