Yellowing of plant

I think i fixed it. I started to suspect it wasn't a deficiency but a nutrient lock that was developing. I started this grow accidentaly with heavy fertilized soil so during the grow i did not really feed until i started to see yellowing of 1 plant. This made me think the soil was getting depleted so i started to build up feeding but this didn't help. There was only 1 thing i fed from the beginning and this was calmag. After looking at my notes, i suspected i overdid it a little with the calmag and this was probably causing the lock. I always bottom-watered because at the start i had lots of gnats so the top layer should still have lots of nutrients. I did a little flush, not a heavy one, just enough to flush out the buildup at the bottom and now i am top-watering with no nutrients. This seems to work, the new growth is having a nicer green color and the leaves with the more yellow tint are also starting to look better. Giving no nutrients at all and trying to utilize the remaining nutrients in the top soil really does the trick. I'm going to select this post as answer so the topic can close. Thanks for thinking with me but indeed it is not easy for you guys if you don't know the whole growhistory.