HI man, It looks to me like it may have been algae, and is now turning into a nice bacterial culture!!, If you have to use a chemical agent to get rid of it, then use Chemi-Clean, FOLLOW THE INSTRUCTIONS TO A TEE, and you'll be alright. IF you want to do it the old fashioned way, I would tell you to do larger and more frequent water changes. I did more water changes and it worked for me, I had to break up the growth of slime first though!
post back and let me know how you make out!! Cheers-Ken