Ok well it looks like I've swapped algae. I went from having bright green fuzzy algae, and long hair algae to this new stuff. It looks like brown-black fuzz which gets a slimy appearance when O2 bubbles become trapped in the fuzz. What is this stuff?? What does it mean? this has all changed as a result of tweaking my lighting regimen. Should I now increase my lighting or do something else?
I bought a bag of eco-complete, and I'm thinking I should cover the entire surface with new substrate and kill off the substrate algae. The stuff on the rocks I can scrub to remove, but what I'm wondering about is whether this indicates a new condition in the tank that I need to worry about.