Is this a Calcium problem?

My whole plant is fine except for a few leaves at eh very top of the plant. My plants at week 4 of flower if that helps. I don't know the PH as i never checked i don't really give it any nutes as i believe the soil i'm using (old horse and rabbit manure) is doing the job pretty well. I do have a little bit of BioThrive Bloom left over from last year and i give it a tsp if that in some water once a week.

What kind of light and how close is it?

hotrodharley said:

What kind of light and how close is it?

Click to expand...

2 mars hydro 300w lights about 16 inches away from the plant.

It'd be weird to have a calcium deficiency in soil. The armchair scientist in me my might suppose that too much light is causing more photosynthesis than the plant can readily supply calcium to maintain. Your tips seem to be pointing a bit up might be a reaction to too much light (way too much and the leaves cup over). Maybe back to the lights off to 22-24 inches.