my plants are getting yellowing from the bottom up and in the first picthe plant on the right is like a light lime green color leaves in stead of a healthy darker green like the one left of it but they are all yellowing and looking like calcium deficiency i dont know if it was over watered at some point causing calcium or nitrogen lock out so i tried to water less so im going back n fourth trying to find the perfect balance to mopisture in my soil also i added some npk to make sure had enough and that it wasnt the problem but still having trouble idk what to do this is my first grow and im just learning as i go as well as getting things i need as i need it.. this is my training learning phase as well as getting everything i need as i need it during this grow so that my next one will be have everything i need in experience and materials.. i know my grammar sucks but please help! the second from last pic with the two blue cups in front of the other 3 those 5 plants are all the same age but only the 2 in front looks like they are doing good but i can see the calium looking defficeny coming along and if i dont fix it i think itll wipe my plant out or keep it stunted like the plant in pic the small plant is an OG kush was looking really nice then out of no where started to stunt and yellow and now has leaves dying off those 3 plants are the same age but still looks like a seedling! will have a ph pen and ppm meter come in tomorrow and i will make sure ph is good i been using rain water which i figured should be good ph level.. anyways thanks in advance guys! this place has helped me learn so much!