I'm also having repeat Cyano problems in my 34 gallon Red Sea Max and am a bit confused as to why. I am using a Fluval 205 with the four foam pads followed by a filter fiber pad, 1 small bag of Fluval brand carbon, another fiber pad, one unit of Chemi-Pure Elite, another fiber pad, one half unit of Chemi-Pure Elite, and a final fibre pad. I usually service the filter every 10 days by rinsing the four large Fluval pads in saltwater. I replace the fibre pads by cutting new ones from the large roll that I bought. I rinse the Chemi-Pure Elite with saltwater and replace once it is three months old. I replace the Fluval carbon monthly. My nitrates are currently 2.5 PPM. Do you guys think I should remove the mechanical filtration from the Fluval 205? If so, all or some of it? 2.5 PPM is low, but not zero. Could that be causing the Cyano?
FYI, other parameters: Calcium is 400 PPM, PH is 8.0, Phosphate is 0.0 PPM, SG is 1.024, ALK is a bit low at 7.0 DKH. Temp runs from 80-82 during a 24 hour cycle. I use Coralife salt due to a belief that it is high in calcium and magnesium while having among the lowest levels of nitrates and phosphates offered by a salt mix. But, the Alkalinity does tend to run on the low end.
I use a DI filter called the Tap Water Filter and change the cartridge when I get more than 5 on my TDS meter. Usually it is 0. I have added a Koralia Nano to the bottom right hand corner of the RSM for extra circulation where I felt like it was lacking the most. I change about 5 gallons of water every two weeks with the DI water that I mentioned. I have reduced feedings to the bare minimum and do so every other day.