There is not much you can do once you burn them, really all you can do is ease up on the feeding. Other than that, giving a plant just a 1/2 gallon of water or feed in a (5) gallon pot every other day, is not the best way to water / feed a cannabis plant. They do better when they are fully saturated, and then they allowed to dry out. Yeah, your plants are telling me, that their are roots in your pots that are never getting watered, then you also have a Mag deficiency that is awfully bad because it has actually worked its self all the way up some of your plants. Anyhow... if they were my plants, I would change up the watering / feeding, and fully saturate each pot, with at least 1 1/4 to 1 1/2 gallons of water / feed (slowly water them until you get a little run-off), and then only water / feed them again, when they dry out, and typically at 2 weeks into flower, that would be every 4th day for a plant in a 5 gallon pot (but that is just guessstimate, lifting the pot and checking how light it is works better, or get a cheap moisture meter and stick it straight down 2 inches out from the stalk, and only water or feed again when the meter reads 2 or less). Also every time you water or feed add 1/2 tsp of Epsom salt per gallon of water to stop the Mag deficiency from prematurely killing anymore of the plants fan leaves!