I had loads when the tank was 12-18 months old, then they dwindled to a handful over the following 6 months. Whilst my evidence is anecdotal, I'm pretty sure it was related to how I fed the tank.
A tank reset is one way of doing it but there is a risk that you get them again and end up in the same situation. Being detritivores that eat from the water column, they only become a plague if you have enough food for them. So my vote would be to try starving them out again. If you feed frozen, make sure its rinsed well etc, and cut back on coral foods like reef roids. Run mechanical filtration / make sure you keep up with changing it out.
If you do all of this already, then I'd be trying to understand where waterborne particulates could be coming from, trapped food breaking down in low flow areas etc. What cuc do you have? Also, are the red patches cyano, difficult to tell from the photos?
Just my rambling thoughts, feel free to ignore!
