The tank should have plenty of flow. Somewhere around 20 times a hour turnover. The tank is 180 gallon with probably little over a 100lbs of live rock straight out of my old tank that was probably approaching 4 yrs old. When the rock was moved into the new setup was a little over 3 months ago. Also quite abit of live sand was used too. Total sand bed depth averages one and a half inches Heres pics of the whole 3 month old setup.
Any ideas as to why this is flourishing would be great.
Did you just add saltwater? Silica can contribute to a bloom. But the thing is if you have used the same salt then it shouldn't be that. Unless you have changed brands I would not expect that unless someone at the plant that makes the salt was having a bad Monday and put a little extra in.
Yes that is Chaeto. Me I like Caulerpa better. I have never had any luck with Chaeto doesn't grow that fast for me. Caulerpa I can watch it grow. Bad thing about the Caulerpa it can go asexual on you and then you have a much bigger problem.
It is more effective to produce unfavorable conditions for the algae you want to get rid of, then trying to use macroalgae to "compete" with it. This is especially true when you have undetectable nutrient levels.
It is usually pretty easy to remove from corals by directing the flow of a powerhead at them.
My advice, do as much manual damage to it by lightly stirring the surface of the sand bed. Yes it will grow back, but eventually it won't. This is how I have always dealt with cyano. You could also try tweaking the tank parameters (temperature, salinity, etc) and see how that works.
I'm definately not the expert on how to get rid of it, so don't qoute me on anything