I've only been adding water with the right pH for a week. Since yesterday, 2 plants are showing new spots. The spots are porous and some are already completely burnt. Humidity is at 55% and ppfd is 417. Please help.

Bugs

The brown, porous spots are most likely the result of an advanced nutrient blockage (pH-Lockout) or a calcium deficiency. If you water exclusively with pure water for over a week, the available nutrient supply in the soil drastically decreases and the pH level starts to fluctuate.

Those are probably deficiencies, not nutrient burn. Plant looks hungry... Water habits look suspect. If choosing a volume in a top-down way, don't do that. Always give as much water as it takes to effectively accomplish the task. under normal circumstances: 1) fully saturage 2) wait for healthy dryback and repeat. when the pot is too big, need to water a smaller area around the plant, but still ensure that moisture goes all the way down or else you are going to train superficial root growth. This also adds a risk of issues in the root zone. When water ebbs and flows it deposits solid nutrients, which then can go back in solution when water returns and potentially builds up to unhealthy levels if repated too often over time. fully saturating is never "overwatering." if fully saturating ever causes a hint of a problem, then the constitution of the soil is poor to start....These are best practices hammered out long before teh hobby of growing a marijuana plant. don't try to re-invent the wheel..

Hey, it looks like you might be just watering a little on the surface every day. If that's the case and your pot feels light, your plants are probably thirsty. It's advisable to water until complete saturation every time, and then wait until the pot is at least 50% lighter before the next full watering. This can take anywhere from 24 hours to a few days or over a week, depending on the plants and pot size. After repotting, it usually takes a bit longer; the better the pot is rooted, the faster the plants will drink the water. You shouldn't let the water "sit" in the soil for too long, as this can lead to anaerobic conditions, increasing the risk of diseases and affecting the pH level, which in turn worsens nutrient uptake. You can also submerge the entire pot underwater until no more air bubbles come out and it feels heavy/fully saturated; this helps eliminate any possible "dry spots" in the soil where it has become hydrophobic. The important thing afterward is to let it dry out until the next watering. Large, well-rooted plants in bloom or during stretch can usually be watered heavily daily, as long as the pot isn't oversized. Otherwise, you can also place the pots in a deep tray that is covered with water up to 1/3 to 1/2 from the bottom and let the plants drink on their own; they will pull the water up through the drainage holes in the pot by capillary action. Good luck!

Hey buddy, take a deep breath. Looking at the heavy, droopy leaves and the overall structure, you are almost certainly overwatering your plant. When a plant is overwatered, the roots suffocate because there is no oxygen left in the soil. This prevents them from taking up water and nutrients properly, which makes the plant look completely limp and sad (even though the soil is wet). Here is how you fix it right now: 1 Stop watering immediately. Do not give her a single drop until the pot feels super light when you lift it up, and the top 2-3 inches of soil are bone dry. 2 Check your drainage. Make sure your pot has holes at the bottom and that it is not sitting in a puddle of runoff water in the tray. If there’s water in the saucer, dump it out. 3 Oxygen is key. Lift the pot up a bit (put it on a grid or some spacers) so air can reach the bottom holes. 4 Be patient. Soil takes time to dry out. It might take 3 to 5 days for her to bounce back. Once she recovers, only water when the pot feels light again. She will survive, just let her dry out and breathe! Good luck!