Problem

Ph fluctuation

At a glance i would suggest mg deficiency if your using coco/L.e.d. it isn't unusual with these in combination, to have to add calmag with your feeds. both leech mg from the plants and medium so we add it back in. It is usually as flower starts and the needs of the feed change for more mg ect..that it presents itself. easily fixed with adding calmag. This won't repair the damaged leaf but will rebalanced the deficiency.

Hi there Jerma, sorry but i have to disagree with the folks here, that's surely magnesium deficiency and it's caused by your too intense light schedule . You gotta reduce the light schedule to reduce the light stress, try uppinh the calmag by making a spray at the same dilution as your feed and spraying the plants twice a week just a short while before lights on. Hope this helps ! :rocket;

Its hard to tell from the yellow spotting on the leaves but if the tips get crisp and 'burnt' that would be overfeeding

Looks like your overfeeding my friend, the burnt leaf tips would have been the first sign.