Yellowing / Brown spots

Are the brown bits dry and crunchy?……… underwatered if they’re not I’d say nute burn/build up of salt. I’d dump a litre of water over the medium with just cal mag added. Or you could use canna flush if you think it’s a build up of nutes in the medium……just make sure it’s not from overwatering or you’ll make it worse 👍🏽

No diary = no information... Your plants look like they've got a potassium deficiency as Roberts said.. and I wouldn't be calling the makers of your nutes for advice on how to water - they don't know what may be in the actual water you use or what your substrate is or anything! They only know about their product. Roberts is right - you need to water with some runoff every time as it clears out salts and built-up nutes that could be building up. My question to you is how do you measure your pH... if you use a meter, have you calibrated it recently? They need to be calibrated frequently. Potassium deficiencies (as well as many other deficiencies) are often caused by a pH that isn't in the proper range. You say yours is 6.1-6.2 which is great BUT if the meter is not calibrated or simply broken, you wouldn't know if this is accurate. I would start there, myself... check the meter, recalibrate it! Once you've recalibrated it, ask it to read the pH of, say, the 4.0 calibration solution... if it does not read 4.0, then you know the meter is broken. If it DOES measure it as 4.0, then you know it's been calibrated properly and can then read the pH of the solution or water that you are giving your plants. And recalibrate it at least once a week... I use my meter twice a day on 3 plants I'm growing in DWC so I recalibrate mine every day or every other day.... Good luck... and start a diary! Even if you can only go back 1 or 2 weeks, diaries give other important information that you might not think is important or relevant to any question/concern that you have but can actually be the key to the solution.

I would switch back to vegging times till problem corrected. 20 to 30 percent of what you put in should go through soil and out bottom. Then take a sample to test it. Ph testing alone can tell you a lot.

Dear Roberts, thank you very much for your long and informative answer. I contacted Remo Nutrients before the grow, and asked if I have to water till run off, they told me I do not have to do that. Should I start watering until run-off? Is there a calculator on how much water I have to give to see your mentioned 20-30% run-off? These are 3 Liter pots, and I water them every couple of days with 500ML of water. There is some run-off on the sides sometimes, due to it being an airpot. Last feeding was yesterday and I gave almost the full strength of the mentioned feeding in the schedule for bloom since I flipped the switch to 12/12 yesterday. Also, I do unfortunately not have a PPM reader 😞.

You have a potassium deficiency or your ph has gotten Out of line. What is the run off ph and ppm? Brown straight tips is potassium deficiency. Now if they were brown and curled up and in that would be nute burn. I am sure someone is gonna tell you that. Are you getting good run off on watering or feeds? 20 to 30 percent. It is like mini flushes to rinse out salts from old nutrition that is used up. If all that stuff is right. She just wants more potassium. I would check the other stuff first. I think your problem is there. 🌱