If it is an Iron problem (see pic below), this might help.
Iron (Fe) Micro Nutrient and an Immobile element
Iron is an important component of the plants enzyme and is also important for the transportation of electrons while photosynthesis is happening...
Iron reacts with many of the components of nutrient solutions, which will cause a nutrient lockup to occur, If you add to much Iron without adding enough Phosphorus, you can contribute to a phosphorus deficiency , so watch out how much iron and phosphorus your nutrients have. The Leaves on the plant can turn a pale yellow along the growing shoots, while the veins remain dark green. When you have pH imbalance, it can make iron insoluble. The tissue between the veins becomes pale or white, kind of mimics the magnesium deficiency, but not yellow, iron has the white where the yellow would be on the magnesium deficiency. The deficiency starts with the lower and middle leaves, while the new leaves become completely lacking in chlorophyll, but with little or no necrotic spots. The chlorotic mottling on new leaves starts first near the bases of the leaflets, so the middle of the leaf appears to have a yellow mark. Iron is difficult for plants to absorb and moves really slowly in the plant.
Harder for outdoor plants to absorb when in hot weather. Parts affected by the Iron Deficiency are: Young leaves and Petioles.
To much Iron can cause a problem that looks like a PH imbalance, Brown spotting on the top leaves, mainly fan leaves. Can affect the whole plant. Iron Toxicity is rare for Ph below 5.5.
Problems with Iron being locked out by PH troubles
Over watering, pests nematodes, not enough drainage, like not enough perlite. High ph, Soils with low iron, High Phosphorus, Excess Zinc, manganese or copper.
Soil
Iron gets locked out of soil growing at ph levels of 2.0-3.5
Iron is absorbed best in soil at a ph level of 4.0-6.5 (Wouldn’t recommend having a soil ph of over 7.0 in soil) anything out of the ranges listed will contribute to an Iron Deficiency.
Hydro and Soil less Mediums
Iron gets locked out of Hydro and Soil less Mediums at ph levels of 2.0-3.5
Iron is absorbed best in Hydro and Soil less Mediums at ph levels of 4.0- 6.0 (Wouldn’t recommend having a ph over 6.5 in hydro and soil less mediums.) Best range for hydro and soil less mediums is 5.0 to 6.0. Anything out of the ranges listed will contribute to an iron deficiency.
Solution to fixing a Iron deficiency
Any Chemical/Organic nutrients that have potassium in them will fix a Iron deficiency. (Only mixing at ½ strength when using chemical nutrients, or it will cause nutrient burn!) Foliar feed with chemical fertilizer containing Fe or rusty water can work well. Other supplements that have Iron in them are: Iron chelates, Ferric oxide, Ferrous oxide, Ferrous sulfate, all of these are fast absorption. Greensand, Cottonseed Meal is slow absorption, Garden Manure, which is medium absorption. Manure is most common organic iron source to use.
Now if you added to much chemical nutrients and or organics,( which is hard to burn your plants when using organics) You need to Flush the soil with plain water. You need to use 2 times as much water as the size of the pot, for example: If you have a 5 gallon pot and need to flush it, you need to use 10 gallons of water to rinse out the soil good enough to get rid of excessive nutrients.
Picture 2-3 is a more severe case of iron def
