heres what you do to get rid of the cyano:
1) determine your water source (tap, RO/DI) You should be using RO/DI. This form of water is purified and contains low nitrate and no phosphate. The cyanos food.
2) increase the flow in your tank. Adding powerheads to get rid of dead spots in the tank, is every bit important as the food we feed our fish. were waste and left over food sit, breaks down into nitrate and phospate, creating sheets of algae, and increase nutrient load in the water.
3) adjust your light time. 8 hours for grow bulbs (daylight) and no longer then 12 hours for actinic bulbs (blue, supplement) This will lower the growth cycle of the algae, eventually causing it to regress because it has no energy source.
The trick with cyano is to follow these steps and remove it when you see it. I would bet a good chunk of money that your nitrates are off the chart, meaning 1 of 2 things. Either your test kit is off, or the cyano is using all the nitrate causing a 0 reading (which isnt a true reading)
Watch the amoung of food you feed and how often. Feed what your fish can eat in 3-5 mins is recommended. Remember fish in a reef feed mostly all day, as in nature, and dont require a larger large amount of food,
following all of these steps and conjuction with your normal water changes, you should see a regression in no time, Id give it 3 solid weeks of removing it when you see it and watching your husbandry skills and you may be in the clear.
Good luck.