What's your pH at?
Could be a micro nutrients issue that some Epsom salt can fix. First check your pH and ppm.
I use 1 TSP per 3 gallons of water, some people use a tablespoon for 1 gal of water. Start out light if you use it
Chill, it might be something similar to microelement facts, like manganese, iron, potassium, and others. Hopefully, use some product for that... microelements.