You have a nutrient issue and your plants aren't getting enough light.
The difference in PPFD between 20" and 30" is huge.
I say that "plants aren't getting enough light" because there's so little foliage on those plants. That's typical of plants that aren't getting enough light but they're not tall and lanky so it might not be too bad.
If you're not getting an Apogee, I'd go with a Uni-T lux meter. In practical terms, a lux meter is as (in)accurate as a PAR meter and far cheaper. I can't make the argument to buy a cheap PAR meter.
The difference in PPFD between 20" and 30" is huge.
I say that "plants aren't getting enough light" because there's so little foliage on those plants. That's typical of plants that aren't getting enough light but they're not tall and lanky so it might not be too bad.
If you're not getting an Apogee, I'd go with a Uni-T lux meter. In practical terms, a lux meter is as (in)accurate as a PAR meter and far cheaper. I can't make the argument to buy a cheap PAR meter.