I started with 4 plants . im a beginner at this 3 of the 4 are growing faster than the 4 th . also some tips are turning a yellow color plants era 8 weeks old , im using a high pressure sodium light 18hours on 6 off ,the plants are in a mylar covered closet with pleanty of circulation im using fox farm grow big plant food in a 20;10;10 soil ph level is at 6.5 average any sugestions would be appreciated thank you
Growth rate gap is probably genetic, assuming they're from seed and growing under the same conditions. Pics would help, along with better details. What is 20-10-10 soil? Sounds like it's synthetically enriched, which would help narrow down the source of your problem. If I were you, I'd learn all I can about nutrient lockout. PH is just one way to lock out nutrients, overnuting and residual buildup in your soil can cause it as well. Your water source is important too, distilled or r/o water can lead to cal-mag deficiencies... probably digging too deep but w/e, just thinking out loud. Diagnosing plant problems is an exercise in the process of elimination, since a lot of problems exhibit the same symptoms. That's why details are so important when asking for help.