Every plant I have grown in Biobizz All Mix ends up having a mag deficiency. Do a search on Goggle and I am sure you will find lots of information about it! But when you water or feed, add 1/4 tsp of Epsom salt per gallon of water to correct your current issue. But, the leaves that have those spots will not recover. You should also foliar feed them with 1/4 tsp of Epsom salt per gallon of water to save as many leaves as you can, because it will take (5-7) days before the added Epsom salt you will add to your watering, is available to the plant!