I would want to ask someone who uses LED lighting and that shouldn't be a problem. Ask how the foiler feed. I would want you to burn your plants.
I haven't grown in soil in idk how long, but if you haven't amended your soil, I would drop the ph even further to get your soil to sit around 6.5.
The direction the plant is going, it isn't going to make it too much longer. 5.9 In 6.5 out, I'd say your medium is around 7.5.
I would flush the soil at 5.5 while foiler feeding. If you can do this every 2-3 days for 6-9 days you should be back in range. Mollase will drop PH as well. If you have Mollase, try adding that to your tea while flushing.
So figure out the best way to foiler feed under LED lighting, and at the same time work on getting your medium back in range. Your plant(s) should bounce back nicely.
I'm wondering what caused the ph problem? Diffrent water source? Do you use well water? Did you ammend with something alkalinity?
These are the things I would do in your situation. I'd also find out about the strength of the lights for foiler feeding UNDER LED..
I hope this helps. Soil, and LEDs aren't my specialties, but the roots must be right, and the plant must get food