Your advice for how to limit nitrate will help eliminate cyano, but it works by limiting phosphate, not nitrate.
Phosphorus provides the frame work for DNA, so it's needed by all nuisance algae and microbes. When one flourishes and another doesn't, it typically isn't phosphate that is the determining factor. It's the other environmental influences that cause one to do well while others eek out an existence. There are many determining factors like, light, flow, other trace elements, temperature, and IMHO, in the case of cyanobacteria, the amount of N2. If you have a sand bed that's pumping out N2, it provides a source of nitrogen that is not available to other problem causing organisms like hair algae. This, in my mind, gives cyanobacteria a clear advantage over hair algae and most other problem causing organisms.
We can never rid our systems of phosphate. It's simply impossible. We utilize many different tactics to remove phosphate from our systems. Like Phosphate removing media. It's a competition, for phosphate, between these types of media (or anything that we use to remove phosphate), and problem organisms with their need for phosphate. The better we are at providing an environment that meets the needs of a particular problem organism, the stronger, and more numerous, that organism will become. As they grow and reproduce, they bind more and more phosphate, robing it from methods we utilize to removing it. This creates a problem if we think of phosphate control as the only means of controlling problem organisms.
As an example. The owner of my LFS tested his new phosphate meter on my water today. It read zero. If I removed all my herbivores today, my tank would be covered in algae within a short few days. Even though my water tests zero for phosphates. We can not control problem organisms with phosphate control alone, because we can never truly rid our systems of phosphate. We must disrupt other aspects of the organisms environment to keep them under control. Anything we can do to disrupt their way of life tips the scales in our favor. With some organisms it's herbivores, maybe it's lighting, maybe it's silica, or flow??????? IMHO, with cyanobacteria, one of the ways to disrupt their way of life is to limit the amount of N2 they have access to. High levels of N2 clearly gives cyanobacteria an advantage. I'd be willing to bet, that even with my zero reading for phosphate, if I added a trickle filter with bioballs, cyanobacteria would begin growing in my system. Properly maintained trickle filters with bioballs don't contribute to the phosphate level of the system. They do contribute to nitrate level though. Nitrate leads to N2, and N2 leads to cyanobacteria.
Don't get me wrong. I do believe that elevated levels of phosphate is a huge cause of problem organisms in our systems. I just believe that problem organisms can do well even if phosphate levels are low, or undetectable with hobbyist level test kits,
if other requirement for their health and reproduction are met. This is simple to test. Just remove all algae eating organisms from a system with a low phosphate level and watch what happens with the algae.
Again, and as always, this is just MHO.
EC
