Definately wouldn't hurt to do up to a 50% water change and try to suck up all the cyano you can while you are siphoning water out. You can take a turkey baster and really blast your rocks to disturb any cooters and put it into suspension to be siphoned out.
IMO Hagen test kits are not that reliable but in any case cyano is said to feed of phosphates. If you are getting a zero reading on your phosphate test kit that is not uncommon in a tank with cyano as the algea is using all available phosphate to sustain itself. As a rule of thumb if you have cyano you have phosphate.
As has been said cut back on feeding and if you are feeding frozen food what I do is let it thaw out in a piece of paper towel and then scrape the food particles into a shot glass of RO water and rinse it a bit and then pour that again through a piece of paper towel and then mix that food with some tank water and feed to tank. Frozen foods are notorious for containing phosphate. With what you have in your tank it wouldn't hurt to cut back on you lighting period. Your probably just fine with your Halides on 4 hours a day or less. I have cut back on the time my halides are on but more for heat control. I just make sure they are on when I am home so I get to enjoy it.
HTH
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