i‘ll mention a few things along this line……..
1. pot plants need and use a lot of 2-3 nutrients, mainly being Nitrogen and Cal/Mag. People tend to stop the veg fertilizer right at the switch to flowering to a bloom nutrient thus causing a N deficiency later in flowering as the plant yellows. I stay with the veg for two week into flowering, then switch to a veg/ bloom 50/50 mix thru week 6. Then a switch to all bloom until the flush. Many deficiencies are also caused by a lack of cal/mag. I use reverse osmosis water, which strips the water of everything so I tend to need more- so I fluctuate between 5ml and 10ml per gallon for ALL water that goes into the plants.
2. use a high grade nutrient, so it does not build up in your medium. Botanicare Pure Blend Pro is 99% organic, not chemical, so it tends not to build up in the soil as much. I tend to fertilize on the lower end anyway, and after week 3-4 in flowering, I’ll fertilize, fertilize and then flush every 3rd watering. All the ferts on the market are generally fine, but watch your plants closely and if you see stuff going on, flush the medium well, let it dry, and reduce your ppm’s moving forward.
3. A lot of issues with yellowing and spotting could be undiagnosed bug and insect issues. Nothing yellows a plant quicker than mites or some of the other critters. As soon as you see something going on with leaf discoloration, investigate and figure it out. Before it gets worse.
Pics are always best if you need help…….