Brown spots? First grow help.

Maybe calcium? but this looks more like you have some bad watering habits. This is soilless, so it's easy as pie... don't over think it. Bottom watering is less than optimal for a soilless method... it basically takes the primary positives and throws them out the window. 1) always fertilize with 10% runoff or more. The runoff prevents buildup. Therefore, any issue you see is a matter of adjusting your formula and nothing else. Makes diagnosing easy. 2) wait for appropriate dryback and repeat -- this will vary as a plant grows into its pot. The same loss of weight = same volume of water needed - learned retroactively, not some pre-ordained volume someone picked out of the ether. 600-750 ppm is all you need to not only feed a plant but let it stock up over time, safely. This is calculated from gauranteed analysis labels and not some EC conversion, which is wildly inaccurate for ppm. EC is important for it's own reasons but only correlates with ppm. There wre free apps and websites that can calcualte ppm based on your labels and dose. Without runoff, you basically trash the superpower of soilless.. it's no longer soilless and more akin to soil. the nutes are still 'hydro' and available immediately, but will build up and will get out of ratio from your formula, which means you also lose control of the rootzone nutrition, potentially. You 'can' make that work but now it's a mtter of occasionaly top-down waterings or not fertilizing everytime and your growth rates will suffer by comparison to a normal soilless grow. bottom feed is fine for soil. shit for soilless even if some people make it work.. you can make a lot of things work, but that doesnt mean it's not contradicting itself in ways that make no sense. Runoff is essential to get near-hydro growth rates from start to finish, and not just for a week or two until shit builds up and gets all wonky in the medium. Won't have the easy diagnosis abiity, either, if you don't have control over nutrition levels in medium, either. those lights are not underpowered... don't over think it... 18/6 at 67-70% power is probably a better spot... may still need to adjust based on node spacing to fine-tune to local variables. hanging distance should be about coverage end-to-end, which is geometry and notmuch else. If hanging distance remains same, it's easy to calculate needs for 12/12 operation, if needed.. 150% more.. so 67% becomes 100% at same distance for 12 hours. most grow lights are designed for these hours of operation (12 and 18) and relates to their suggested area of coverage for vegetative and flower phases... don't reinvent teh wheel. you can get imaginative when tryingto cover a much smaller area early on with seedlings to save watts, but once you are dealing with the full footprint, keep it simple.