Very light green leaves and curling down

Yellow interveinal or from tip of leaf and encroaching inward? if from tip-in.. From bottom of plant and working upward? If so, this is nitrogen deficiency symptom*. by curling down -- like an upside down canoe or like a claw? Assuming no watering issues, a claw is a sign of too many nutrients. curling down on sides can be heat-related. ** All of this is just reference material you can get from a leaf chart. it'll seem difficult to use at first, but once familiar with various symptoms and how to discern them, for example mobile vs. immobile by where the symptoms present themselves can help eliminate possibilities. Recent behaviour is key. substrate? correct pH? balanced feed relative to your growing setup? pH is key to consistency. a drastically different pH needs a different mix of nutrients for optimal growth, if possible. soil - 6.8 (slightly acidic being key), soilless 6.5ish, hydro lower .. say 5.8 but i am no expert there. after that react to plant. adjust nute mixed based on leaf chart. Don't change it ever time.. need time to see impacts of change. balance is key... there's no magic bullet to feeding... agood system should provide what it needs, relative to substrate. super soils and living soils are a slightly different dynamic.