[reeferaddict]

I'm thinking they're Dinos dude. Diatoms are usually cyclical and can result when tank conditions are changed suddenly. Introduction of silicates is key to the success of diatoms and some people have actually dosed silicates to allow for diatoms to become the dominant algae as they are easy to get rid of. Basically once the silicates are consumed you can scrub, scrape or blow diatoms into the water column to be skimmed away. Also, there are quite a few natural grazers of diatoms.

Dinos are a plague however. From the look of your gravel shots I am guessing you have dinos. They overgrow large areas and smother other life very quickly forming stringy gooey stinky kinda clumps. I've actually been extremely fortunate to not have these, but I have had every other damn kinda algae, and from what has been said earlier on, you are probably best to go that route. I have read of so many posts on here & other boards where this pest is truly a hobby killer, especially if it is recurrent.

After much hard work to rid my system of pest type algae, I am happy to scrape the diatoms and green algae off the glass twice a week. I never have to worry about this on my rocks or such though. Try running your Alk a little higher for a couple of weeks to see if that may help. Skimming is more efficient at higher alkalinity and pH, but who knows if it will do anything for Dinos...