Those holes and yellowing look to me like potassium deficiency. You might want to look for some dry ferts from one of the SnS guys or GLA etc. It's cheap and you can then adjust your dosing to whatever method you choose to follow, be it estimative index or PPPro. That scum is probably rotting bio. I wouldn't worry too much about it yet. You can add an air stone and churn the water with it for 30 minutes a day to break it up, and then when you do your water changes it will go with the waste water. That light you have is less than ideal from what I gather from others who have them. You might want to ramp up the photo period to say 9 or 10 hours a day.