Yellow leafs

Localized root-zone hypoxia. Having air intake on one side of a indoor grow will create uneven areas within your tent, uneven levels of oxygen and co2 movement/distribution which can in turn cause very different symptoms progressively over time, even when all plants are fed/treated what seems equally. Its definitely cal and mag related but more from the creeping ph skew caused from the medium running out of oxygen on one side of the tent. I'd be checking my soil temps across the pots, soon as oxygen goes bulk flow goes and cal mag goes with that, if soil is oversaturated above a point oxygen will move so slow it's essentially "locked out" even if your medium has optimal porosity. Oxygen locks out, everything shifts from aerobic to anerobic, atp per glucose molecule drops from 48 to 2, acids begin to skew ph, bulk flow stops which stops 100% of cal and mag, bulk flow delivers cal and mag for free without a atp cost attached, as soon as you kill bulk flow , all calcium and magnesium now has a atp cost attached to uptake. Only problem is the plant no longer produces enough atp to do much of anything other than survive. Everything else is just a symptom imo. Gluck

It is not a magnesium deficiency......................cal/mag is not the universal cure! Unless your pH is below 5.5 or above 7.5, true nutrient "lock-out" is almost impossible to get.

Burning from over feeding................typical biotab/greenhouse issues. Next grow, use liquid, cannabis specific fertilizers and avoid issues. Over the last 8 years of being involved with this site, biotabs seem to cause problems regularly.

make sure your ph is correct. if that is then its magnesium deficiency and u should add a little Epsom salt to your waterings

Hey there! Based on the photos, there is a clear yellowing (chlorosis) on the lower fan leaves. This is very common in week 2 of flower when the plant finishes its 'stretch' and needs energy, but the roots are struggling to absorb nutrients. This is usually caused by one of two main issues. To figure out which one it is, you should check:Nutrient Lockout (Salt Buildup): If you have been feeding heavily (especially with flowering or PK boosters), mineral salts might have piled up in the soil, blocking the plant from absorbing Magnesium and Nitrogen.pH Issue: If the pH of your water isn't regulated, the roots get locked out and cannot take up food, even if the nutrients are present in the soil. How to fix it right away:Flush the soil: Water heavily with plain, pH-regulated water (between 6.2 and 6.5 if growing in soil) to wash away the excess salt buildup from the root zone.Check the runoff: If you have the tools, measure the pH and EC (Electrical Conductivity) of the water coming out of the bottom of the pot.Cut the dose in half: For your next feeding, cut your nutrient chart doses by half to avoid overloading the substrate again."

Not much information to go off here but I would suspect it’s a PH imbalance causing a lock out, the lockouts then cause the plant to leech nutrients from the leaves. The lockout is likely a mobile nutrient as it’s showing on lower growth. High root zone temps with saturated soil can cause PH issues. You want to minimize stress to the plant during the initial flower stage if the plant is stressed your flower development will suffer. If you can pick up some cold pressed kelp or kelp extract and Foliar feed it while you wait for the soil to dry out. You’re in in a light mix soil, are you letting it completely dry out between waterings? If not then I suggest you do this asap. After 2 weeks in flower when you’re back on track you can remove those affected leaves and monitor the new growth. Have you checked the PH and EC of the water you feed. You should also make sure to use cold water 18-20c maximum as within a few hours in a warm tent the water temp will rise. Warm water doesn’t contain much free available oxygen. A good method to add oxygen is mixing nutrients in large bottle with a lid. You can shake the living crap out of it with loads of bubbles and froth plants will love it. I personally use a bucked and measuring jug I pour the mix violently to mix it making sure there is loads of bubbles. Hope that helps 👍

Looks like Fe deficiency based on pattern of chlorosis and starting low on the plant, but that would be kinda rare... trace elements are more often locked out rather than physically deprived in the soil. Plants don't look toxic, so make sure pH isn't going crazy. Make sure you are providing some Fe if it's not a soil-grow (check labels). More than one thing can cause interveinal chlorosis starting at lower and middle parts of plant (at least somewhat mobile nutrient at play) ... usually something stands out when you assess what you have provided over time. Eliminate possibilities with the full context of your grow that you couldn't add to this question.