Dropping like flies HELP

[chevcam]

I have a well established tank about a year now. And I consantly check my water condition about three times a week. I have a 90 gal reef with 50 gal sump. water readings as follows..... Nitrate- below 10 ammonia 0 nitrites 0 SG 1.025 temp 79 Ph 8.2 My problem is in the last two days I have lost 4 fish ..Orangeshoulder tang..flame angelfish..2 blennys within two days??? I checked water right after and still looks great, all my other fish including three shimp are eating well and look healthy. Is there any thing else I need to be testing ?
Sign stummped

 

[acekjd83]

were there any visible signs of disease? reddened gills, spots, abnormal behavior, overt aggression or territoriality? recently change food or notice anything different in food?