Brown spots on upper leaves

Appreciate the help, I wish i could pick multiple answers as the "solution" because I think yall nailed it. topping up with full strength lets it build up and I hadn't gotten a clean res in weeks, makes total sense. Swapping the res out for a new one and i'll be topping off with half strength and watching my ec ppm more.

Your EC is to high at 2.3EC on an auto, autos like lower feeds and can not handle higher dose feeds as much. This is cauing it it burn under the light as its taking up to much. Keep using the ratio of nutrients you are giving them, but dilute the EC down to around 1.5-1.8 and give it a good amount of runoff in each feed if it gets runoff. This helps prevent salt buildup. if it does not get runoff, give the resviour a quick change of water and feed. The light is weak and should not be causing any issues, I have used a bunch of 18w mini led strips before totalling 90W and then could touch the light and be fine. Not saying this is the same but you could try and find out the PPFD of your light from the manufacturer then they may have suggested hang heights. PH of 6 is fine, 18/6 is fine, Temps could be lower but not a huge deal. Good Luck!

You are experiencing slight light damage and a little bit of nutrient burn. I recommend you definitely raise your light another 6 inches or train your plants down another 6 inches to help with the damage on the top of your canopy. The. Lower your feed from 1200 ppm down to like 900 and I bet your plant will thank you immensely. Also your humidity wasn't listed so I can't determine your VPD which could also be an issue. Hope this helps

Hello my friend, your pH is too high for hydrophonics. You want to bring it down to pH 5.8 And you are overfeeding the plant. Cut back the nutrients from 4ml per liter to 3ml per liter. This should be enough!

I think its overfed mainly PK. Thats 4th week of blooming and it looks very bushy, got huge amount of energy to do that. Especially when looking at 3rd week, its just exploded.. At this point, try use lower doses of ur fertils. Once u overfed with P/K it could wipe out Ca and Mg. If its that, the next days would show new signals of brown dots and more slowly yellowing leaves. Use water with source of Ca and Mg but without PK... By the way, ur plant is very impressive

ph low 6's. 18/6 light cycle.