If you are maxed out height wise at 5 weeks what is going to happen when they stretch and double in size? I have 3 Ak-47s and a NL on day 19 of flower. They have not doubled yet but have increased 90%. You may want to think about scrog or LST. When I flipped, the tallest was 12" and held down with major LST. How tall are your plants now?
Light tips may be nutrients, light or like @kdawg said an adjustment to the new light. I grow in a 3x3 with 450W. Others do it with a lot more with out CO2. Increasing air intake and flow within the tent can help. You can check them out at An auto, three photos and a clone
\Good luck
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