Might this be a Calcium deficiency I'm having...

hey man your plant is having trouble growing, it could be any number of things but certainly those brown spots are calcium related. Calcium and magnesium are used to regulate photosynthesis and with 90W's worth of light and such an otherwise healthy plant, the plant is stuggling to grow. Those leaves take a lot to maintain you know ! so in the meantime while you're waiting for your new light, lower your current light to around 15/20cm depending on how close you can get it, seems close but it will help. at lights off, spray cal mag something like 3ml/L to 5ml/L for most brands once a day at lights off. uptake by the leafs is 85% efficient, uptake by the roots is 15-25% efficient, you do the math ;-) the problem should stop spreading within 10 days and hopefully by then the new light will come. Hope this helps ! 🚀