Nitrogen. Probably the most common cause is overwatering. If the soil feels wet and the pot feels heavy, that’s probably it.
Looks like you sprayed with diluted DE with H2o and it dried
why are you using DE on the plants? Insect issue? If just silica for the soil, it should not be on the plant. Do you have mites, thrips, gnats, white fly…other?
Get yourself an oven sprayer bottle “new and clean of course” jet spray the leaves, put a glove on and gently rub off the DE unless you still have bugs! Dilute some aloe vera with spring water and spray it 1st thing in morning. Allow to dry completely dont overdo it…then when it dries you’ll have white film on the leaves as well, so if you want you could even clean that off after it dries.
Probably nitro, check ph runoff, fix if nessasary and throw a handfull of fresh pearlite that should do it.
If your pests have an exoskeleton use de earth, you must let your topsoil dry completely, wad up tp and dust your fans, leave 72 hours flush out check ph and correct if nessasary. Witch you are allready doing however if the dust gets wet it will not work correctly.