You might be watering with alkaline water. If you have hard water, then you are putting down a little bit of dissolved limestone every time you water. Can you find out the pH of your water supply? Here in Madison, Wisconsin, our city supply tap water has pH around 7.6. I add 12 fluid ounces of regular white vinegar(5% acidity) to 4 gallons of tap water, and this is used on our blueberry plants. Since vinegar is slowly consumed by soil bacteria, I also apply granulated soil sulfur around the shrubs, which lowers pH over time. I don't think that it is possible to correct iron chlorosis unless soil pH is lowered to the optimum for the particular affected plant.

I have the same problem with my citrus trees. I use an iron chelate. It is much easier than fighting the pH of my soil.

Sequestrene 138 and Sprint 138 work in soils which are high in pH, calcareous, or have heavy clay which tie up iron.

It works great for iron chlorosis but it is not cheap. I got mine for around $80 for 5 lbs.

Whoo. You weren't kidding about the price!
The liquid I have been using has chelated iron and chelated copper.
Why is one tree great and the other not?

There could be many reasons why one tree is doing better than the other. Maybe one has root damage from a gopher or root rot, maybe one variety needs less nutrients, maybe there are pockets of soil that are different enough to cause different nutrient availability, maybe they are growing on a different root stock?

I have three citrus trees planted three feet apart in my yard. I feed them all the same. The washington navel orange is always dark green and rarely shows signs of chlorosis while the lisbon lemon and clementine mandarin almost always show signs of chlorosis in the spring. I don't know why three similar trees planted so close together act differently. When I fertilize them in the spring/summer they all become dark green.

Citrus are a heavy user of nitrogen and a full range of micro nutrients. Citrus are the only trees in my orchard that get a synthetic fertilizer, one labeled for citrus. Al

AHa. So I am not the only one with persnickety trees.
I went out last night and sprayed the liquid iron on the leaves. Will see how things go.Thanks all