Glue Gelato Auto BARNEYS FARM

So after last weeks flush I have developed brown spots on the upper leaves. am i right in thinking the plant need cal mag? i have never used it before now. but is on both my plants. anyways i bought some and have just given its 1st dose of it with phd water. seems to be on the leaves that had the claw and only the very top of the plant. other than this the buds seem to be growing nicely and have plenty of trichomes covering them. Also starting to get sticky. i have also installed my new tsw2000 which has bumped my heat enough so i can take out my heater. temp stays around 27c. could this also have brought up my problem? my plan is to give ph water with cal mag for couple days before starting the nutes. this seem like the right action? any advice is much appreciated