Didn't know about the coco. Make sure your using a coco formulated nute in that case, other than that can't speak much to experience with that medium. Use Ph 6.0 water and use same process, but I'm guessing your ph is low locking out that stuff. Had that issue myself in the past.
I agree, test EC if you have the opportunity also.
It looks like you have some type of lock out. My guess is your medium is too acidic? I would just flush for this next week. Do you have any clearex or final phase? I suggest doing a flush of that and nothing but fresh water into it. It looks like it's getting pretty serious. No use in giving her food if she can't eat it. Wasting money at that point, imo.
You're right, you don't want to wait, you want to fix it and move forward. What would you say the PH result is? I can't say but its low eh. If you want to flush it right and be done with it, flush it with 6.0 (assuming this is your desired PH?) with about 3 x the water of your grow container and then give it 1/2-3/4 str feeding. Put in your desired PH, get out desired PH, introduce nutrients of your desired PH. I wouldn't recommend putting 7.0 into a medium that is reading 5.0 hoping it would average to 6.0. Pump the 6.0 through her until you know its 6.0. This is the advice that was given to me by members here when I encountered the same issues except with soil, the turnaround was faster than I expected. This happens to everyone at least once too, so don't beat yourself up over it, its a learning experience.
Flushing is very annoying, I hear you PT. You'll want to go with 3x the size of your grow container so if you're in a 7 gallon you'll want 21 gallons of flush/runoff. Once you get the desired PH, then you can give some food.
Good luck bro!
My best guess is evaporation/plant consumption. You ph your water with acid each time, so the input is correct but when it evaporates or water is taken up by the plant the acid can remain. (it can actually also be eaten by the plant as a food but that's another topic) Just make it part of your regular practice to measure runoff at minimum twice a week and you will avoid issues into the future I think.
Hell yeah the HPS burnt your plant...I can't get mine cooled down either, so I am going to use my MH through this whole grow, or maybe the HPS a few hours, probably not at all...
I would be inclined to guess that salt buildup pushed his PH too acidic. I totally agree, keeping up on runoffs is a great idea but without EC readings it would be difficult to tell what is forcing the PH too acidic. The best way IMO to ensure you're not getting a salt buildup and that your plant gets plenty of nutrients at the correct PH is to water with plenty of runoff. Something I would definitely do with coco if I were using it. When I used synthetic nutes a friend of mine suggested to water until 30% of the water I've given the plant has run off. This simulates a pseudo flush every time you feed to ensure you're applying appropriate PH and plenty of food while forcing residual food from the substrate to maintain PPM's in your desired range. I did this with synthetics in soil and had awesome results by feeding every time I watered the plants. I collected the runoff, metered it for PH and PPM compared to the solution going in. I aimed to keep it within 20-25% and under 800-900 ppm for soil, some strains like it lower or higher. Never used coco so I don't know what you aim for, probably a bit higher. I got a little crazy with it recording a bunch of data but I learned alot from it. A nice addition to any garden for 20-30 bucks is an EC meter. It can help figure out what's going on in the substrate when you encounter problems.
No prob PT, I'm stoked to hear they're back to business! I hope its smooth sailing form here out.