Yellow leaves on the top of the plant flowering stage

Hi everyone,
I'm at week 3 of flowering stage and I noticed my plants started to get yellow from the top of the plant around the buds. I grow in Coco coir 7 liter pots I try to water everyday depending on how much the plant has drinked sometimes I give less water and sometimes more up to 600-700ml. I pH at 6.1 everytime and was last feeding at 1.6 EC at week 2 then I sprayed them with a product called (STOP GROW) because the plants where getting too high and the next day they where fine until I watered again with 1.6 EC I saw the plants started yellowing a little bit and I tryed to flush with plane water and now all my plants are almost with yellow leaves from the top like on the picture. Also I had a problem with my light that I saw after a couple of hours my light bulb was going on and off maybe they are just stressed and reacted like this. Can anybody help me out since this is my first grow. Thank you very much!

The plants looked like this after I watered with plane water now at day two they look even more bad but I can't take pictures because of the lamp

Two things:

one-- check for root aphids they turn leaves yellow especially NEW growth. Best way to do this is by smacking the sides of the pot and to turn up the dirt a bit and look very very close to the inner edges of the pot and see if they come out.

Two-- add some potassium silica to your plants this can also give plants a yellowing issure especially during any type of heat waves the plant may be experiancing. Some strains act differently in regards to heat and potasium silica can help solve this.

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Looks like sulfur deficiency. You could mix 2 teaspoons of Epsom salts in a gallon of feed and see if that fixes mew growth. I don't believe the leaves currently affected will ever go back to their original green.
Doesn't look like heat problems or wind burn, but both are possible.