While I believe you are probably just loosing some emmersed leaves, (or have a nitrogen problem) here's a good diagram for figuring out plant deficiencies.
* Symptoms: New leaves are distorted or hook shaped. The growing tip may die. Contributes to blossom end rot in tomatoes, tip burn of cabbage and brown/black heart of escarole & celery.
* Sources: Any compound containing the word 'calcium'. Also gypsum.
* Notes: Not often a deficiency problem and too much will inhibit other nutrients.
* Symptoms: Older leaves, generally at the bottom of the plant, will yellow. Remaining foliage is often light green. Stems may also yellow and may become spindly. Growth slows.
* Sources: Any compound containing the words: 'nitrate', 'ammonium' or 'urea'. Also manure.
* Notes: Many forms of nitrogen are water soluble and wash away.
* Symptoms: Slow growth and leaves turn pale yellow, sometimes just on the outer edges. New growth may be yellow with dark spots.
* Sources: Compounds containing the word 'magnesium', such as Epson Salts.
* Symptoms: Small leaves that may take on a reddish-purple tint. Leaf tips can look burnt and older leaves become almost black. Reduced flowers or seed production.
* Sources: Compounds containing the words 'phosphate' or 'bone'. Also greensand.
* Notes: Very dependent on pH range.
* Symptoms: Older leaves may look scorched around the edges and/or wilted. Interveinal chlorosis (yellowing between the leaf veins) develops.
* Sources: Compounds containing the words 'potassium' or 'potash'.
* Symptoms: New growth turns pale yellow, older growth stays green. Stunts growth.
* Sources: Compounds containing the word 'sulfate'.
* Symptoms: Poor stem and root growth. Terminal (end) buds may die. Witches brooms sometimes form.
* Sources: Compounds containing the words 'borax' or 'borate'.
* Symptoms: Stunted growth. Leaves can become limp, curl, or drop. Seed stalks also become limp and bend over.
* Sources: Compounds containing the words 'copper', 'cupric' or 'cuprous'.
* Symptoms: Growth slows. Younger leaves turn pale yellow, often starting between veins. May develop dark or dead spots. Leaves and shoots diminished in size. Failure to bloom.
* Sources: Compounds containing the words 'manganese' or 'manganous'.
* Symptoms: Older leaves yellow, remaining foliage turns light green. Leaves can become narrow and distorted.
* Sources: Compounds containing the words 'molybdate' or 'molybdic'.
* Notes: Sometimes confused with nitrogen deficiency.
* Symptoms: Yellowing between veins of new growth. Terminal (end) leaves may form a rosette.
* Sources: Compounds containing the word 'zinc'.
* Notes: Can become limited in higher pH.