Grapefruit Auto (1st Grow)

Very stressful week for a 1st time grower🤦‍♂️ But I remain optimistic🤘 What I first believed to be nutrient burn from water splashing on the leaves when feeding, I now believe to be a CalMag deficeny after more research. I'm using hard water so I assumed it would be high in cal and mag. Due to this I added very little CalMag at first. After upping CalMag she grew very well with no new signs of deficency for most of the week, then after the top of the soil became dry she started to show deficeny signs rapidly. I gave her a little more water with only Calmag in it to see what happens. They start out as shiny spots in between the veins on the leaves. Then within a couple days the spots turn from shiny to yellow and the leaf begins to dye. The deficeny seems to only appear on the lowest growth until it dies then the next node gets it. If anyone has any tips or you think I have made the wrong diagnosis please let me know. I'm very happy with her growth, by the end of the week shes just as big as before defoliation. I'm just concerned if I cant get this deficency in order there wont be any leaves left😬 Again any help is greatly appreciated🤘