Saltgator, I have 25 fish, mostly wrasses, in my 115g cube. I believe my tank is very balanced at the moment. SPS are very happy, parameters are great, no cyano or nuisance algae besides some bubble algae. I am able to maintain this with a quality skimmer, micron sock, prodibio bioptim/biodigest, and I use microbelift special blend and nite-out II (following maintenance directions on bottle). I also have a separate rock rubble area in my sump with an additional 25lbs.
IMO bacterial stability is the determining factor of what bioload your tank will handle. Adequate surface area for nitryifing bacteria to populate is very important. Rapid conversion of Ammonia and Nitrite in heavy stock tanks is a must to keep a system flourishing. IMO you must do this without creating a nutrient sink to keep it working optimally. Tanks with too much rock in display, too little flow, dirty sand beds etc… don't function as efficiently. This is why I opted to keep less rock in display and have a separate rubble compartment. Water passes through micron sock before the rubble so detritus is minimal.
To answer your question, I use cyano as a gauge that I have too much bioload at that given moment… This is not to say that stocking threshold has been reached. Several weeks or months later your system may develop more bacteria to cope with more fish and eliminate cyano.
Don't know if I am right or wrong in my explanation, but this is how I make sense of things
Here's a quick tank video with a small feeding
[video=youtube_share;ibA3w2pJhXo]http://youtu.be/ibA3w2pJhXo[/video]
