I have a 55 gallon reef that's been established for around six years. My pH is around 8.1 to 8.3 my calcium is 480 nitrate, nitrite .0, ammonia .0, phosphate .0 to .2 I do 10% water change every week and everything has been great but for the past week I've had brown spots coming up in my sand. I've had and kept the same regimen for 6 years expect this past week I used reef chili 3 times to feed my corals. Do you think this could be the problem? My sand has always been bright white now it looks burnt. I light with a fluvle 2.0 pro for 8 hours of light 4 hours of moon light and 12 hours dark. Any ideas of what could be wrong would be greatly appreciated.