Patch on Leaves

Looks like light stress to me. The top leaves are pale lime and some tips are yellowing, which is typical when the canopy sits too close to the light. Your EC and pH look fine, runoff EC is a bit below input so the plants are eating normally. Raise the light or dim it until the top of the canopy is about the distance your manufacturer recommends, and tuck or train the tallest tops down. New growth should come in darker green within a week

20cm distance with the spiderfarmer sf1000D is really very close.. I have it too and it can't be dimmed.. your plant will still grow a bit more. Even if it's a nutrient problem, you'll get too close to the lamp🤔🤗

It would generally start with interveinal damage on top-most leaves.. Since some of the colas quite a bit further are showing similar, i'd wager more nutrient balance related. Whehter ~1.5 EC indicates high concentration depends on how much the water is adding... only need 600-700ppm of fertilizer to feed a plant in a soilless/hydro context. I second the no-foliar ... it's an option for extreme cases, but much beter to learn how to properly feed through roots and simply avoid ever needing a filiar feed. just not enough info to give a simple answer with confidence...

These are the signs of long term over feeding / nute burn. The plant does not need "foliar feeding".

Sometimes the leaf tips can look like this just from overwatering. try cutting back on how often you water and see if that helps. if you normally water every 3 days go for 4-5. Just see how your plant responds to drying back if it gets worse then you know its more nutrient saturation than watering issues. Also environment may be a little too dry For how hot it is. The plant may be working harder than it needs too. Maybe adjust the intensity of the light down 5-10 percent too.

We are seeing a report of the last few weeks. Back your light off a bit. Here you need a foliar spray for immediate uptake. Algae nutrient is a good one. Also a nice balanced mineral fertilizer mixed 12-25% strength for foliar feeding. Better to start weak and see how they react. Then keep checking that everything is in range and adjust as needed. Something similar happened to me recently. I know how much of what to use for what after many grows. One day my plants were communicating with me telepathically, getting a little sick yellow. I was like, wtf? Why are these plants being dramatic? It wasn't dramatic like my Golden Mosaic can be. Its a tropical plant from Brasil. If the humidity isn't right, it goes straight into drama queen mode! Leaves turning safety-yellow color, then the leaves go crispy tan brown, necrotic spots and leaf tips burn. But like yours I was seeing something is not right... So I started testing again. Runoff is ok. Soil, its ok. No bugs. Lets retest my usual solutions....Viola! 💪Something had changed. I don't know if its the city water that changed or my supplies are getting old and need to be replaced... but the numbers were not like they usually are, not how they used to be. Surprised me. The plants told me. Anyway, keep watching. Bypass rhizome problems and feed them directly through the leaves until you get everything dialed in. Then wait and watch. 2 weeks.

It's nute burn but doesn't look bad we use this as an indication to what's going on and what she can handle nutrients wise...balance it out n grow on