just another take on this.. from the looks of your tank from what i can see you do not have hair algae but some type of macro. you don't have a lot of coral in there. I would remove the rock. pull off as much of the macro as possible and toss it... then i would bleach the rock in a bucket for a couple of days with some good circulation. then do a vinegar bath for a few more days this will kill anything on or in the rock. while killing the rock I would manually remove all the giant aptasia from the sand bed with a 3/4 " tube. this will get them out before they can expel any thing. I would then add 2 peppermint shrimp to the main tank and one to the fuge. do not disturb your sand bed just yet. leave it there to act as your biological filtration while your rock is out.. you can clean the top layer of sand with a smaller siphon tube. this will get rid of most of the detritus and most of the little aptasia in the tank. replace this with fresh salt water. give your peppermints a couple of weeks and they should remove any and all aptasia that are left in the tank. after the vinegar bath rinse your rock in some ro water for another day. do a second dip in ro and replace back in your tank. while your tank is going through this feed very sparingly. it will keep the detritus down which feeds the aptasia and will also encourage your peppermints to eat the aptasia instead of the food. your tank is small enough to try this first. this way you won't have to get rid of anything. you won't upset the tank and hopefully you'll get rid of all the nasties. it will also prevent your tank from going through any huge cycle.. good luck in what ever you do..