Notes on Sulfur Deficiency in Plants:
Sulfur is a macronutrient. 
- Symptoms:
- Old growth is green, but new growth is pale yellow all over. Lower fruit production.
- Sources:
- Epsom salt (magnesium sulfate)
- Notes:
- More often a problem in weather that is dry. Sulfur protects against some types of fungus. Sulfur isn’t used in germination. Sulfur helps with deterioration of the seed casing, but this does not apply to aquaponics. Embryonic roots use sulfur to grow strong. Lowers pH, which is good for peppers.
- Warning:
- Commercial fertilizers might add heavy metals, or other chemicals that will poison your fish and possibly you.
Photo Credit: http://en.wikipedia.org/wiki/Chlorosis