It might be early potassium deficiency, but itβs mild. Give the plant a few days to respond to the increased Alga Bloom.
Early potassium deficiency signs
-Color loss starting at the edges of the leaf (margins fade first).
-Leaves turning a dull, washed-out green or grey-green.
-Tips and serrations sometimes slightly yellowing before browning later.
-Often shows up during early flower because the plantβs K demand jumps.
-Your leaf fits several of these.
But keep in mind: this can also be caused by
1. Light stress
Leaves directly under intense LED light often show:
-Pale topside
-Slightly bleached edges
-Uniform desaturation without necrotic spotting
If this leaf is from the upper canopy, check your PPFDβit might be a touch high.
2. Mild magnesium deficiency
Magnesium (Mg) deficiency can show:
-Pale areas between veins
-Overall desaturation
-Sometimes misidentified as K deficiency
Mg needs also increase in early flower.
3. Soil/feeding mismatch
You said you're using Alga Bloom 4 ml/L. BioΒ·Grow/Plagronβs Alga Bloom is organic and slower-release compared to mineral nutrients. Itβs not uncommon for organic feeds to lag behind the plantβs sudden K demands when flower begins.
Meanwhile:
-Keep pH 6.2β6.5 for proper K uptake
-Make sure light isnβt too strong on that leaf
-If it spreads, add a small K booster or a bit of Epsom salt for Mg support
Right now it doesnβt look seriousβjust monitor and adjust lightly. Hope that helped! π