Sulphur deficiencies are uncommon in hydroponics because most fertilizers contain enough that it’s rarely ever an issue.
If sulphur is deficient the plant will experience overall stunted growth. Leaves grow slowly and are smaller and narrower than usual. Stems grow tall and lanky instead of bushy. Buds are slow to develop and can die.
Sulphur is an immobile nutrient. Plants cannot relocate sulphur to support new shoots and leaves. This causes symptoms to show up on the new growth first.
A clear indicator of sulphur deficiency is yellowing of the new growth that starts at the base of the leaf and moves out toward the tips.
Sulphur deficiency also causes stems to turn purple.
A sulphur toxicity stunts the plant. Foliage turns dark green. The leaf tips turn brown.