If those were caused by spider mites you would see webs on the plant by now. I doubt it's spider mites. Unsulfurred molasses is the cheapest way to supplement calcium/magnesium. Plus you get good sugars and other micro-nutrients for the soil. Blackstrap is a name brand that many people use but you can use any so long as it is unsulphurred. You need to be aware that molasses can act like a booster for other nutrients. Like anything, start slow and move up the dose. 1/2 teaspoon / gallon to start. All good then move up to 1 teaspoon / gallon. And remember, damage done is damage done. Look to the new growth to know if the plant is recovering.