Hi. My friend having hard time with his plants. L...

PH Up. Flush with better ph water. Let her reset

Garentee the soil ph is off. Is the soil being used fox farm happy frog if so that soil starts at a ph of around 4 and will cause lockout every time when used 100% happy frog. If your not useing that soil. I wld guess you are adding to much

Alkaline soils can cause certain nutrients, such as iron, manganese, and phosphorus, to become less available to plants. This can lead to nutrient deficiencies, resulting in symptoms like yellowing leaves (chlorosis) and stunted growth.

I don't see a diary. So, its really just a guess by gong what you say above 3ml/l is too much by the sounds in a med soil.. Less is more with growing. Lower feed to 1ml/l and feed less, once every 6 days or so, feed with low calmag and a root stim or something organically benifical for soil.

had a very similar issue with my current run, bumped calmag, controlled ph etc without results. started using bibioz acti vera and the issue went away (leaves with necrosis wont get back to green tho) https://www.biobizz.com/producto/activera/ This has a lot of micronutrients that, even though unlikely, could be the cause of the issue as well. happy grow, mate.

Calcium mag. More than likely a overfeeding of nutrients. If he says he has been feeding every day, is that regular tap water is it? Most people's tap waters run alkaline a over 7.0, What is it though when we say alkaline... just means it's full of "mineral salts". Calcium, Magnesium, Zinc. When we fertilize we leave it up to the grower to decide if they want to add cal mag generally because your tap water has often enough in it already. We all love to give a little extra cal mag just incase, makes it a very easy mistake to make. Calcium is a bitchy nutrient in that it doesn't play well when in excess, it starts to interrupt uptake of other nutrients which can present as deficiency of other nutrients when it's just high levels of calcium. First off before anything you need to get a accurate pH first in order to guide what to do next. Excess amounts calmag no doubt ph is high. Aluminum sulfate is very fast acting natural ammendment you can add to water for acidicfying the soil. I use it regularly to great effect. You could also flush flush flush and reset the soil but by doing so you will wipe out most nutrient based on their mobility within the soil. Nitrogen as Nitrates+ is extremely mobile in soil, Nitrogen as Ammonium- is extremely immobile in soil. Ammonium over 30% is no no no. Get your ph back in line and should be ok.

Lotta of other useful information missing. Lights, how long and how close? PH. what is it going in and out? EC how much going in and out? Watering how often? His medium is soilless peat with some worm castings in it, this should be watered with runoff, so it could be a PH issues of calcium getting locked out or a buildup issue. Looks like N and Mg is also at play here. Check your buddies feeding regeme and confirm its getting enough, if it is, then work on PH managment and runoff. https://www.biobizz.com/wp-content/uploads/2021/03/Nutrient-Schedule-EN_2021-1.pdf