Hi All, I am getting back into the hobby. Make a long story short, I moved my old nano (10 gallon) to a 120 gallon tank in a school lab since my fish outgrew my tank and I thought students would enjoy it about 6 months ago. Unfortunately, the 120 gallon tank is failing. The walls of the tank are covered in red algae (cyanobacteria?) The beautiful colorful algae on my rock is gone...There is brown algae on the live rock. The reef lighting was moved to a freshwater tank!!!! (I am hoping this is moved back tomorrow). The live rock (there is a ton of it in there) looks gross. My goal is to clean that tank and get it up and running well again. THen eventually restart my nano down the hallway in my old ten gallon tank. I hope to at least save my remaining corals. The 120 has a 20 gallon sump, protein skimmer, and I think a bag of carbon. The tank has two large wavemakers in it. I do not know if that is enough flow. I have not really had a chance yet to examine the entire system in detail. My first question is how do I clean it? I am thinking about scraping red algae/slime off all of the glass and then do a 50% water change. (I am setting up a 50 gallon trash can with distilled water and sat next to the tank so that the people in charge of it can easily do water changes every week and fill a 20 gallon tank with distilled water and hook up the ATO to the sump.) The tank is in an ideal spot a few feet from a distilled water system and several drains. The person who set it up invested in high-quality stuff. I do not think RO/Di is an option especially with investment in the distilled water system. I have only worked on my 10 gallon nano for 2 years, but I have never dealt with this kind of bacteria/algae or protien skimmer. I will try to post pictures tomorrow. thank you!