White spots on the leaves, yellow leafs(5) , and red stems

Looks like a cal mag issue or a ph issue. Would start there

what kenough+asnoriu said just want to say ph balacing does not need to be expensive. once again, stay away from marijuana branded companies. they are often unknowledgeable about common manufacturing processes in the Ag industry. they lack common production knowlege and/or cut corners and price gouge. read the ingredients. the expensive ph-down is just citric acid or acetic acid... or maybe a concoction of a few common acids. just buy the cheap version of the ingredient and not the marijuana branded ph-up or down product.. those are no different atom-for-atom. which acid or base you use is not going to reduce drift. if the fertilizers you use are not ph-buffered, drift will occur because they were made wrong. soil nutes are different. they expect the soil to mitigate ph-issues, but for any hydro/soilless nutrient lineup, if it drifts in pH that is a shit-ass fertilizer. ph-drift shouldn't occur. it's a sign of poor choices in production, lol. Extreme contexts of some weird microbes causing it would be very rare and usually wouldn't be able to budge a buffered product. whether i add my nutes to 8.4 or 7.0 tap water, it comes out to the right pH everytime. It does not drift in my reservoir at any point. You won't often have to ph-up, but you likely have some 5% acetic acid (white distilled vinegar) around the house. get some 3-5mL pipettes for easy measurment. you won't need more than a few mL per gallon.

It’s a Magnesium chlorosis. Your light is too close and/or too intense ! Back up your light or lower the dimmer. Study the Chlorophyll and the photosynthesis, you’ll learn that magnesium is the central molecule of the process and why your plant start to reflect the blue and red spectrum of the light making those purplish stems, veins and petioles.

To me, this looks like phosphorus and accompanying calcium deficiency, with bright red stems, brown spots, and yellowing leaves in places. Deficiency might not be caused by the lack of those nutrients in the soil since you seem to provide everything that she could ever want. The issue as @AsNoriu said might be low PH. At PH levels below 6.2, the phosphorus uptake becomes basically nonexistential and as Phosphorus and Calcium interact with each other inside the plant it might cause more issues. PH can be tricky to balance especially on a budget and I haven't grasped it fully myself. Hopefully, it's a simple fix with BIO PH+ and she recovers very quickly since you caught the issue really early.

Your ph is off, way lower than should be, plant struggle with uptake, rusty spots - aka calcium deficiency. Maybe lack of potassium. For coco in FLOWER - ph 6.0-6.2 For soil in any stage of grow target 6.3 Maybe your pen lies, maybe needs calibration. Good luck !