Can you help ID this please !!

Hello!!

I am very new to this. I actually purchased about a month ago an established aquarium. It's 48g with about 40 lbs of LR. She had this aquarium set up for about 2 yrs she said. I reused the same water & LR when I transported to my home and reset it up. I did not take her live stock, but did end up with a few snails and bristle worms. After the second week, my nitrate & PH levels were good so I added one small blue Hippo and one small Percula clownfish. The last week my rock started turning a brown(LR was a pretty red) and now has this weird stuff growing on it. I'm noticing it growing on other other LR as well. Could someone help me ID what this could be? I showed my LFS but they were unsure what it is. What clean up crew would help me out best?
Also I do not have a sump system, just a Aqueon 55 that hangs on the back of tank. I just changed out the two filters with new ones a few days ago and have been doing 1-2 weekly 5-7 g water changes to help reduce nitrate levels

 

can't see the actual algae - but from your description it sounds like turf algae

 

sorry not sure why my pic's are so small

 

Are you sure it isn't cyto?
Xtalreef

Near the bottom