If your tank has been running for a while which it looks like it has I believe you would have noticed the Phos much sooner. If you feed your livestock you will have Phosphate and Nitrate no way around it, it is a matter if your system can deal with the quantity. Brown Algae can be from many things, lighting to Silica in the water, if you keep running the GFO it should help if you have any Silicate in the water. Cyanno is a Bacteria and is most of the time a sign of Detritus build up, if you can try and increase your water movement within the tank or change it around some and see if you can get more movement. The idea is to try and keep butt much Detritus suspended in the water column so as it breaks down it can be swept away into your overflow.
If you are using any type of prefilter clean it every 3 days max or use filter sock 3 days max. BRS just did a review or small experiment and found that 3 days max change out would help reduce Nitrates longer seemed to start to add to it. Like I said, you should readjust the skimmer, lower the water level, from the bottom of the cup and up you want to have the big fluffy bursting bubbles and roughly pea size in the neck just below the bottom of the cup, you should see a much darker and thicker/chunkier skim begin to be produced.