What the actual heck is going on with these leaves

sounds liek lockout, pH issues, ratios of nutes given.. etc etc... back off. irrigate water only for a while. you are in vege, so this is no big deal, unless on a tight schedule. EC is a good guesstimate and that's high enough that a problem could be occurring due to it (ec doesn't measure elemental ppm, so it can be off by a bit) I bet it;s a P toxictiy basedon picutre but... you almost certainly have to flush, so it doesn't matter what it actually is at moment. move away from FF nutes. soil is soil as long as they don't put a heavy amount of wood chunks and large particles, lol. FF is hot soil (if you used it), so if you fertilized regularly a bit early, it would easily build uo.

Is this mostly on the bottom leaves? new growth? Usually, the bottom-most leaves start to get a little crispy or yellow as they start getting old. If your dryness problem is just affecting the oldest leaves that don’t get much light anymore, you likely don’t need to worry. After your plant has grown a few sets of leaves, it’s very normal for the first few sets of leaves to turn yellow and die, especially if they’re not getting light anymore. Or the burnt tips on leaves can be an indication of nutrient burn. This will be widespread as over-fertilization affects the whole plant. Small, burnt tips are common and nothing to worry about. When the yellowing intensifies and advances, however, it is time to take action. Once leaves start to curl and go brown, they are definitely goners. Nutrient burn can be gradual if the overdose is only slightly stronger. It can also be rapid-appearing, progressing over a few days. The worst-case scenario is a chronic overdose that causes crop-wide yellowing and wilting overnight with leaf curl and lack of turgidity. In this case, if during the vegetative phase, start again. Recovery may be impossible or take longer than restarting completely. Buds can be affected by nutrient burn as well. During the flowering phase, cannabis changes the way it uses nutrients. The need for nitrogen drops almost to zero while the demand for other compounds like calcium and magnesium increases. An overdose of any kind of additive will cause the same type of burning features. Hope this helps!