eek what's happening?!

Fix your temps. If you can't do that I would get a silica supplement like Protekt to use along with your regular feedings which can help strengethen plants agains heat stress and cold. Get a ph meter and some ph down. Adjust to 6.3 or 6.4 or 6.5... Whatever... But just make sure your consistent with it whether your giving nutes or plain water it doesn't matter. ALWAYS as adjust. Don't worry about testing run-off ph as it is not accurate and you'll always see something different. Test what goes in, adjust accordingly, and you'll be fine. As was said above, lime in soil will help, although most good soils have lime or oyster shells already in it... If not... Add some. It will help to buffer ph. When feeding fox farms nutes 1/4-1/2 strength is fine as long as its enough, but do not go half on the calmag if your using filtered water. Thats something that needs to be fed as recommended as your water is likely being stripped of most of that.
I bet you anything your plants are having difficulty uptaking nutrients because of major ph and temp swings. Fix this first instead of adding more of this or more of that because all your going to do is end up with salt build up from adding tok much crap trying to fix deficiencies when all you had to do was feed/water at proper ph. Again, as someone said above, flush with ph 6.5 water, 2-3x the volume of your pots and then start feeding/watering with consistantly ph'd water each time. Feed recommended doses of calmag. It should resolve itself.