Cyano

Wondering what else I can try to get rid of Cyano bacteria growing in my tank, I use NSW and have been doing weekly water changes, I've also adjusted the flow in the tank multiple times during the last month but it just keeps growing back all over the substrate and live rock. Was only a small patch I planned on siphoning out before I went on a week holiday back at the start of July, but got back and it was 1/4th of an inch thick in some parts.

180Litre tank, stocked with 1 clown, 1 Fire Gobby, 2 snails 2 hermits. Protein skimmer running 15 hours a day, lights on for 6/8 hours a day.