it must be oil.. u look up from bottom its bery clearly seen.. my tank do have oil also no much harm on LS or Coral. An overflow box will be better on removing the oil.
its ok to mix fish and reef.. which i think all of the bros are doing.. but do take note on what fish are u adding.
Refer to this chart.
http://www.liveaquaria.com/general/compatibility_chart.cfm
since u living in the west side i do have 1 fish trap for sale can get me by leaving me a pm or 93677669. its really not adviceable to use medication on marine fish especially into the main tank