There are a million and one posts on it. Cyano is the redish mat you see on your rock sand and even on your back glass I think. It is caused by too many nutrients, too little flow, and too much light.
First look at your feeding schedule. Your fish should be able to eat eveything you give them in 1 or 2 minutes. There should be nothing falling to the bottom of the tank. If there is you are feeding too much.
Then the lighting schedule. Your lights should normally run on for about 8-10 hours per day with what you have in there. If you have them on longer cut back.
Flow is improtant in your tank. It looks like you have one pick up tube in the tank so I am guessing you have a hang on the tank filter. consider getting a power head to put inside the tank to move water around. This will help to keep the nutrients in suspension in the water column for removal by your filter. How often are you cleaning your filter material? You need to replace the material at least every week with your water changes.
How often and how much are you changing your water? With the cyano you have you should be doing at a minimum 10% every week. You would be better off doing more until you get the tank clean.
When you do a water change take a turkey baster first and blow your rocks. This way the detritus (garbage) on your rocks will go into suspension again for removal by your water change and your filter. When doing the change use a siphon tube and suck up the cyano. It will come up very easily like a blanket being sucked up.
Do some searches and read some more on cyano. Whatever you do don't be persuaded to use any chemical means to combat it. This is only a bandaid at best. You need to address the root cause and correct it.
Hope that helps a little.
