Squado, im pretty sure ur having cyano
. Yes they are really crazy. I tried blacking out the tank for 2 days, they were gone. The 3rd day, after the light was on for an hour, it came back even stronger lol. Google cyano
and how to get rid of it.
I'm not sure unstable pH would cause this. PH will change from morning (lights on) and at night, (after lights out). Sounds more like excess nitrates or phosphates. I think it might be hard to detect phosphates because the cyano lives off of it.
PH changes very lil between light on and off, about .1 or .2. By unstable PH, i meant going from say 8.1 is the lowest ur PH should be, to 7.8 like squado said his PH is. If he tests PH when light is on and PH is at 7.8, PH could be 7.6 at night, which is not suitable for a reef.