patience,patience patience it was just last week you posted this give it some time buddy and it will dissappear.your lights being out will help but wont fix it.dont bother with your tests for nitrates or phos chances are they are undetectable because they are not there or are just 2 small to read up on our crappy tests especially phos.
it happens in all tanks at some point in time for different reasons some of which we will never know for me i had a bad problem with spawning from snails everytime a brew was hatched i had an outbreak i didnt notice the cause untill the snails were big enough to see and i finally put 2 and 2 together, so when ever i seen an outbreak i knew i was expecting baby snails.
decaying matter is a huge feul for cyano alot of time when a snail dies or shrimp or fish or what ever and doesnt get found it rots this feeds the cyano.the amount of nutrients these dieing animals produce is too small for our test(unless its a huge fish) or we dont have a test for it(like animal spawing/reproduction/birth)
one thing is for sure if you keep doing what your doing it will dissapear but it needs to be manually removed or your just playing a longer waiting game for something to starve.
chemicals work but remember that this isnt algae its a bacteria and a very resiliant bacteria at that and its only function is to survive and popuate...thats it ....and one thing weve learned about our world over the centuries is bacteria will find a way no matter what happens....nature finds a way
cyano is a magician it dissappears today for todays reasons just to appear tomorrow for tomorrows reasons.....best you can do is make it uncomfortable for it by keeping clean water,lots of flow and killing off its food source.
your doing all the right steps so it will dissappear and since this tank is only around a year old its still quite young in the reef sense and prob will battle lots of this stuff in its time to come.
running carbon and gfo aggressively in a reactor will also help your case and wouldnt hurt in the long run an yways against the battle for controlling nutrients.
give it a month or so and keep doing all you can cyano is battle thats easy to win but also gets the best of people by not being patient and trying to many "band aid " fixes.
cheers buddy
and good luck