My Tank is cursed...need help!!

[Amadod2]

Hello everyone, so my tank is acting up, over the last 1.5 months i noticed that my corals are bleaching, not all of them just a few,i do have a chiller and i even reduced the amount of time my lights are on,3pm till 10pm. i have checked all of my levels and they aren't bad, but i have been neglecting my tank a bit as i just started night school. So my Alk is at 8.5 and cal 490, last water change made April 30, and i do use filter socks but haven't changed them in a few weeks....like i said i been busy. i have now removed the filter socks and i am preparing to do a water changed tomorrow. Any idea of why they are bleaching??? og and my temp is set to be no higher then 80 with the chiller on