This is a very helpful chart i saved from another post here RIU ":
Yellowing of Younger leaves............. Fe, Mn.
Yellowing of Middle leaves................ Mo.
Yellowing of Older leaves................. N, K, Mg, Zn.
Yellowing Between veins................. Mg, Mn.
Old leaves drop................................ N.
Leaf Curl Over.................................. Mg.
Leaf Curl Under................................ K, Cu, Over Fert.
Leaf tips burn, Younger leaves........ B.
Leaf tips burn, Older leaves............. N, Zn.
Young leaves wrinkle and curl.......... K, Zn, B, Mo.
Dead areas in the leaves................. K, Mg, Fe, Zn, Mn.
Leaf growth stunted........................ N, P.
Dark green/purplish leaves and stems......... P.
Pale green leaf color..................................... N, Mo.
Leaf Spotting.......................................... ...... Zn.
Spindly........................................... ............... N.
Soft stems............................................. ....... N, K.
Hard/brittle stems........................................ P, K.
Growing tips die........................................... K.
Stunted root growth.................................... P.
Wilting........................................... ............... Cu.
Use this chart as a reference ONLY. This is not a guaranteed diagnosis of your plant and you should only use this as a guideline to help you figure out what your nutrient solution is lacking...
ELEMENT and Description of Deficiency and Toxicity
N (Nitrogen) .................. Deficiency: Plants will exhibit lack of vigor as older leaves become yellow (chlorotic) from lack of chlorophyll. Chlorosis will eventually spread throughout the plant. Stems, petioles and lower leaf surfaces may turn purple.
Toxicity: Leaves are often dark green and in the early stages abundant with foliage. If excess is severe, leaves will dry and begin to fall off. Root system will remain under developed or deteriorate after time. Fruit and flower set will be inhibited or deformed.
P (Phosphorus) ...........Deficiency: Plants are stunted and older leaves often dark dull green in color. Stems, petioles may turn purple. Plant maturity is often delayed.
Toxicity: This condition is rare and usually buffered by pH limitations. Excess phosphorus can interfere with the availability of copper and zinc.
K (Potassium) .......... Deficiency: Older leaves are initially chlorotic but soon develop dark necrotic lesions (dead tissue). First apparent on the tips and margins of the leaves. Stem and branches may become weak and easily broken.
Toxicity: Usually not absorbed excessively by plants. Excess potassium can aggravate the uptake of magnesium, manganese, zinc and iron.
S (Sulfur) .......... Deficiency: The initial symptoms are the yellowing of the entire leaf including veins usually starting with the younger leaves. Leaf tips may yellow and curl downward.
Toxicity: Leaf size will be reduced and overall growth will be stunted. Leaves yellowing or scorched at edges.
Mg (Magnesium) .......... Deficiency: The older leaves will be the first to develop interveinal chlorosis. Starting at leaf margin or tip and progressing inward between the veins.
Toxicity: Magnesium toxicity are rare and not generally exhibited visibly.
Ca (Calcium) .......... Deficiency: Young leaves are affected first and become small and distorted or chlorotic with irregular margins, spotting or necrotic areas. Bud development is inhibited and roots may be underdeveloped or die back. Fruit may be stunted or deformed.
Toxicity: Difficult to distinguish visually. May precipitate with sulfur in solution and cause clouding or residue in tank.
Fe (Iron) ........... Deficiency: Pronounced interveinal chlorosis similar to that cased by magnesium deficiency but on the younger leaves.
Toxicity: Excess accumulation is rare but could cause bronzing or tiny brown spots on leaf surface.
Mn (Manganese) .......... Deficiency: Interveinal chlorosis on younger or older leaves followed by necrotic lesions or leaf shedding. Restricted growth and failure to mature normally can also result.
Toxicity: Chlorosis, or blotchy leaf tissue due to insufficient chlorophyll synthesis. Growth rate will slow and vigor will decline.
Cl (Chlorine) .......... Deficiency: Wilted chlorotic leaves become bronze in color. Roots become stunted and thickened near tips.
Toxicity: Burning of leaf tip or margins. Bronzing, yellowing and leaf splitting. Reduced leaf size and lower growth rate.
B (Boron) .......... Deficiency: Stem and root apical meristems often die. Root tips often become swollen and discolored. Internal tissues may rot and become host to fungal disease. Leaves show various symptoms which include drying, thickening, distorting, wilting, and chlorotic or necrotic spotting.
Toxicity: Yellowing of leaf tip followed by necrosis of the leaves beginning at tips or margins and progressing inward. Some plants are especially sensitive to boron accumulation.
Zn (Zinc) .......... Deficiency: Chlorosis may accompany reduction of leaf size and a shortening between internodes. Leaf margins are often distorted or wrinkled.
Toxicity: Zinc in excess is extremely toxic and will cause rapid death. Excess zinc interferes with iron causing chlorosis from iron deficiency.
Cu (Copper) .......... Deficiency: Young leaves often become dark green and twisted. They may die back or just exhibit necrotic spots. Growth and yield will be deficient as well.
Toxicity: Reduced growth followed by symptoms of iron chlorosis, stunting, reduced branching, abnormal darkening and thickening of roots. This element is essential but extremely toxic in excess.
Mo (Molybdenum) .......... Deficiency: Often interveinal chlorosis which occurs first on older leaves, then progressing to the entire plant. Developing severely twisted younger leaves which eventually die.
Toxicity: Excess may cause discoloration of leaves depending on plant species. This condition is rare but could occur from accumulation by continuous application. Used by the plant in very small quantities.
Thanks to King Kron from another board."
