Need help

Several possibilities here. PH to high, RO used with no cal/mg. or not enough. Over watering, getting the right nutrients. Some strains are very light in green color especially new growth. Try Cal/mg foliage light spray cocktail 2hrs before light.😎

Looks like the lights are a bit too bright, IMHO

Just looks like newer growth to me.

it's occuring at the top, so that tells us it is immobil. Referencing a leaf chart there are more than one possible cause. p-tox and k-tox both cause interveinal chlorosis with new growth. thinner leaves tends to occur, which may or may not be happening in that picture i cannot see well, but another indicator , if so. K is disctinct by how it spreads across the leaf tips (all around the serations not just at the end of the leaf tip, whereas P wil lmostly burn at the tip) both can lock out the same stuff, so coinciding Mg or Ca deficiencies are possible too. If you use some wildly different bloom formula, i'd consider that when looking for a cause. what 'they' say is often based on regurgitated nonsense.

With no information it is hard to say for sure. Looks like light is too strong for stage of growth. Again detailed information or a diary would help to figure it out for sure.