Why 18-18-18? That is definitely not the ratios that plants use N,P and K so a large proportion of that fert will be wasted and probably end up polluting some water body.
Can't see why fertilizer would help with chlorosis which is usually brought on by high pH or low iron unless it is acidifying fert or contains high levels of iron.
Treat low pH with acidifying fert to reduce pH back close to neutral an the locked up iron will be available to the plant. Adding extra iron, especially chelated iron which is acid, will give extra in the soil so the plant can get enough even with high pH so chelated iron is often recommended for chlorotic plants.
Yellowing of the leaves, either with or without green veins, can have several causes. Not just an iron deficiency in the leaves. However, chlorosis with green veins and no spots is usually an iron deficiency.
And even if it is caused by an iron deficiency, it indeed doesn't mean there is a lack iron in the soil.
It can also be a nitrogen or manganese deficiency. When leaves appear deficient, it is often good to look at if the nutrient is mobile by seeing if the symptoms appear on the new or on the old growth.
If a nutrient is mobile, most plant species will break down for chlorophyll in old leaves, and transport the nutrients to the leaf tips. Meaning, old leaves will appear chlorotic, but new ones won't.
If it is not able to do this, then the old leaves will stay green and the new leaves will be chlorotic.
For example, nitrogen usually is mobile while iron is not.
Chelated iron usually is pretty safe to apply. Just figure out which dilution to use. EDTA or EDDHA doesn't really matter too much, but EDDHA will be preferred but also more expensive. EDDHA is a more effective chelating agent and thus has a wider pH range. It should be taken up even through the leaves.
Fe2+ itself is a Lewis acid. It can precipitate out a small amount of -OH, resulting in a shift towards more H+, raising the acidity, lowering the pH. Not sure what the pH of a Fe2-EDTA solution would be. EDTA is basic. And it specifically prevents Fe2+ from precipitating with OH-, or anything else.
I was able to unintentially trigger chlorosis in some of my trees by using a system anti-fungal this summer. It can be brought on by not enough fertilizer - or too much. Water pH too high, or too low. Too much water. Not enough light. Etc.
