Deficiency

Nutrients made for hydroponics works great in soil.

Keep everything as mentioned in the nutrient sschedule maybee add 1/4 of N , as the plants stretching and recovering from your training methods like topping , they use more nutrient . Also it is normal that signs of deficincies appear through that process . Also your pots seem to be dirty with excess nutrient which should be washed away . So maybee try to spray pump them and clean the watertrays afterwards then put them in ph neutral water to let them soak water and clean the bottom , to get rid of more excess nutrient. If you plan to transplant once more before flower , you dont need to clean the pots. Make sure to not veg to long with small pots , since they dont have much water and nutrient buffer in flower the bigger they get . 15l is good for 7weeks of Veg in my Opinion. You should Defoliate the plant at this point since there is too many leafs in some spots , maybee take out lower leafs which are already yellowish ,since it takes the plant more energy to recover them , instead of just growing some new ones in higher better spots. Also this reduces nutrient uptake , since the plant doesn't have to fuel the big leafs on the bottom which at this stage are covered anyways by higher ones reducing photosynthesis and giving more strength to the upper cannapy growth . Keep Care not to trim to many leafs , a good way of guesstimate would be that the earth in the pot shouldnt have much light at all , I prefer to clean out the lower 1/4-1/3 of the plant at this point .

It appears that you're still vegging your plants. If you've been using cal-mag, stop. In its place, add 1 teaspoon of epsom salts per gallon of water. No other nutrients for this watering. Water until run-off with your magnesium rich water. You may need to repeat it one more time. If you do, add the epsom salts to your nutrient feed routine but don't use cal-mag during veg. Old leaves that already show the deficiency will not heal. You will know you fixed the problem when it no longer progresses. Once you switch to flower, then stop with the epsom salts and start using cal-mag. Its during flowering that your plant requires the most calcium. I never use cal-mag during veg unless I see signs of calcium deficiency while my plants are still vegging.

Does seem like a magnesium deficiency.............could be due to using hydroponic nutrients for soil cultivation.

More details would be helpful. The leaves show magnesium since you have the beginning of zebra stripes on what appears to be the lower part of the plant .... older fan leaves. For whatever reason, your plant isn't able to uptake enough magnesium. Your soil may be deficient of the mineral. However, lockout can also cause it too. The extra details would be ... how old is the plant? The grow media you're using. What is your nutrient routine, pH of the media, watering habits, and have you been using calmag? Closer up whole plant photos from the top and side would also be helpful. With the little bit of information I have, I can tell you (again) your plant needs magnesium. With the extra information I requested, I can pretty much sort out whether its deficient or lockout.