Leafs turning yellow

Not enough info to determine cause. VPD info would be nice aka, temp and humidity, daytime temps and night temps. Nutrients used and strength of mix would be nice. And your pH of your mixed nutrients and water when you do water. Nutrients of choice? Don't water on a set interval. Water when the plants need water, and not before. Feel the weight of the pot. If it feels light, then you water. Determining a problem isn't always easily identified by a few pictures. Pictures, coupled with the info mentioned above, will give you a much better chance of the actual issue being identified and advice given to resolve it. But with next to no info anyone that gives you an answer based on those pictures is just guessing at best. Unless the problem is super obvious, like a potassium deficiency.

I usually use CalMag Agent from PLAGRON and thats always helps me with this.

Have a hard time seeing they are running outta food since they transplanted into 7g pots 2wks prior to flower and only in wk3. Only use bottle spring water since I’ve had Ph issues in past. 300w mars hydro is at 75% 24” above canopy. I did have it turned up to 90% when issue started but hasn’t seem to get better since lower it back to 75%