What would you do?

[Frenchie2]

My bio cube (29 g) crashed a little while ago. So I am starting basically from scratch again... Cleaned the tank, put some live sand I bought at the LFS, put some awesome looking live rock from another reefer who had it in its sump for quite a while along with 1/2 the water from his existing tank (pristine water conditions) in order to kick in the biological cycle a little faster, then the other half with new RODI salted water. Put a couple of small power heads for more circulation and then wait a while before I put the fish and left over corals (lps) back in there. Well everything was peachy keen, water parameters excellent and everything looking good after a week. Then, I notice some damn hair algae starting to grow here and there. I have omitted the day lights all week, just left the actinic on for 9 hrs/day. Can't believe it! F#¥@ hair algae! I got a cleaning crew (25 blue leg hermit crabs - little wee ones) and they are working away but the algae is still growing. I scrubbed the rock with a wire brush, but it's still growing.... I performed a couple water changes (15%ea). I also put some Rowa phos & Purigen in the back chamber (middle) right off the bat. Is this going to go away? What else should I do? I am so tempted to just get rid of the rock and put some new one in there, but will the same thing happen again? Please advise