Cool MBL, In cooking the rocks you have allowed an ammount of detritus/end product to shed from the rock, you woud have to leave it thier for a long long time to get it all. By looking at the rock it looks like the sheding process is still on going, the algae is johnny on the spot to soak it up as its coming out as Witful and Curt have said .
With the rocks sitting directly in the sand it means they have more crude then then should, so this is probibly way its still coming out. Think of it this way, just the fact they are sheding and you are removing it is a big plus, better then it sitting inside building up. heres a couple things for ya.
>keep blowing off the rocks and make sur you get right inside the hair algae to. also keep a good maintenance schedule on syphoning out the stuff on the bottom of the tank.
> I would get some astrea snails, they will eat the algae and poop most of it out, but you have a better chance at removing thier poop with skimming and such then by trying to harvest the algae.
> if you can increase the flow a bit more to keep the detritus in suspention and allow it to get out of the tank that would be great.
> it doesnt look like you have any fish so if you then I would imagine you dont feed, if you do I would cut right back on thier food for a while until the porblem subsides.
Do you add anything to the tank?? additives or any types of food?? what kind of salt do you use??
Mike