Any idea what's going on here? I've put ...

definitely Ca excess week 6 from ur Diarie canna coco a = 7% * 11//4.7*0.713=114ppm SHOGUN Cal-Mag = 3,2%* 3.8/4.7*0.713=18ppm that's without ur water ppm (how much ppm IDK?) so 140ppm+water (Ca?)= Ca excess only if u aren't using osmose water wich i think u don't BAM 😎 all those burning tips, yellowing from top and Mg lockout is the cause of (Ca excess)

Buy a PH stick! they arn't expensive , then all your issues will be solved

It sounds like you're already taking smart steps to address potential issues in your grow. Raising the light to reduce heat and light stress is a good move, especially if you noticed signs like leaf curling, tacoing, or bleaching at the tops. Cutting back on nutrients is also a reasonable precaution if you suspect nutrient burn, which often shows up as brown, crispy tips or very dark green leaves. Since you're working on a budget and don't have a pH meter, you're at a slight disadvantage when it comes to diagnosing potential nutrient lockout due to pH imbalance. Without proper pH control, even if you're feeding correctly, the plant might not be able to absorb nutrients efficiently, which can cause strange deficiencies or slow growth. If possible, picking up some inexpensive pH test strips or aquarium test drops could be a helpful addition to your setup. That said, it's also worth considering whether your nutrient reduction might have gone too far, especially if you're now seeing pale or yellowing leaves, which can indicate underfeeding. Environmentally, make sure you're maintaining good airflow and not overwatering, as both can lead to additional stress or root issues.

Week 5 was OK, I did notice some windburn on a couple leaves which indicates she is a little stressed from high air flow. Week 6 is when you start to notice tips going yellow, this is indicative of your medium getting a little too much mineral salts (high ec). This will need to be lowered through leeching. As soon as plant starts to suffer osmotic stress, calcium is the first nutrient to be effected given that calcium is generally uptaken through passive flow of water. Ph most likely drifting a little high too, this will also effect uptake.

ph would impact ca before other stuff, so good chance that's not it. does look like light damage, but also some blueish hue to those leaves? could be p-deficiency or just related to blasting leaves with light beyond what it can handle per day.. if that is the case. it doesn't look like you fed heavily, so i'd get that back up to normal and see how it goes... as long as it trends in a positive direction you'll know it was the light within a few days. you can buy a 100-pack of ph strips.. get the ones with 0.5ph resolution and that's good enough. as long as you aren't ocd about it, it's plenty to spot-check for 2-4 years for 5-7 USD, lol they'll 'expire' before you use them all.