I wanted to share my experiences with cyano (red slime bacteria) and how I am knocking it back naturally. One of my main goals in this 2nd go around with keeping a SPS reef tanks - I wanted to base my decision making on observation rather than test kits and chasing numbers. I wanted to avoid the use of reactors (GFO / Carbon) and the use of chemicals (chemiclean, dosing vodka, etc). My tank/Feeding characteristics: 310 gallon Morning: 1/2 block of PE Mysis, 1/2 block of Bloodworms, around 1/2" square section of LRS Reef Frenzy Afternoon: 12:00 and 2:30 PM Autofeeding of a mix of Dainichi Baby Sinking Pellets and Spectra Thera A Evening: 1/2 block of Mysis, 1/2 block of Reef Cavier, 1/2" square section of LRS Feeding Frenzy Every two days I feed a 1/4 sheet of Nori. I occasionally feed reef nutrition Live Phyto, Rotifier, Oyster Eggs. That's all shared with: 2 Ocellaris Clownfish, 1 Bangaii Cardinal, 1 Copperband Butterfly, 1 Hippo Tang, 1 Sailfin Tang, 1 Tomini Tang, 7 Lyretail Anthias (6 Female 1 Male), 1 Swallowtail Angelfish, 1 Helfrichi Dartfish, 1 Purple Dartfish, one skunk cleaner shrimp, one mccosker flasher wrasse and one Katherine's Fairy Wrasse So I am really feeding alot and need to deal with the organics / detritus to maintain a healthy system. I have two barebottom tanks that are currently showing severe signs of cyano. My 310 gallon (Total water volume = 360 gallon) which has been running for about 5 months now. I also have a 150 gallon (total water volume = 175 gallon) that has been running since 2014. Anytime anyone ever posts about having cyano - the two most frequent suggestions on cause is Phosphates and Flow. I'm beginning to suspect this is a myth or not entirely true. The 310 has the following flow characteristics: 2 MP 60 on each wall and two MP 40 running on the back wall running at 70% Tidal swell for the majority of the time and a once a day 90% run for 2.5 hrs. The turnover of the tank is estimated to be around 4000 GPH through two Waveline DC 12000's running at 65% through 4 returns in the tank. This tank has ~ 200 pounds of Pukani rock that was thoroughly pre-cleaned and cured. The 150 has the following flow characteristics: 2 MP40's running on each wall at 65% and one MP10 on the back wall running at 90%. Turnover is ~ 1500 GPH with a vectra L1 running around 65%. this tank has minimal rock work and So from above, I have massive flow and turnover occurring in these two tanks but still have cyano on the glass, rocks, frag racks, overflows. When measuring phosphates, for the past three weeks I have been reading zero on a salifer test kit. there's no blue tint at all from these samples. This is similar to other reports from other people having similar issues. I skim wet as well: Nyos Quantum 300 in the 310 and a Nyos Quantum 220 in the 150. Clean those out when I change filter socks. So I can't answer the question as to what primarily drives cyano to grow like this based on these observations and the other posts of people having similar issues. We all have good flow and measure zero phosphates with test kits. What I think might be happening? If we insist on saying phosphates is the root cause: is it a form of phosphate that doesn't get detected in hobby grade test kits? Is it just an overall nutrient problem that's not detectable with hobby test kits? Is it purely organics and phosphates were a side effect? Possibly yes to all of the above. As to how I am beating my Cyano? This all started occuring (or has been occuring) with the following maintenance routine: Filter socks changed once every three days A water change every two weeks. Over the July 4th weekend - over 4 days - I wanted to perform large water changes to try and stabilize the tanks and eliminate this issue. I performed 45 gallon water changes on each day (over 4 days) to the 310 gallon and 25 gallons on the 150 gallon. So in total over 4 days I changed out 180 gallons from the 310 and 100 gallons on the 150. I noticed this had no effect on the cyano occurring in both tanks. So I made changes to my maintenance routine. I am now changing out water once per week instead of every two weeks and I am changing the filter socks once every two days instead of once every three days. This has really improved the look of the tanks and I see the cyano is receding. So through mechanical instead of chemical means - I am beating the cyano naturally. I have no before/after pictures to back this up. It's only the observation that I'm making in my own environment.