ishar, anything that may damage roots, leaving too few for the uptake of nutrients, may cause chlorosis, it's not just an iron issue alone.

Having said that, in looking I find coconut coir is near neutral in pH (7.0), and that's not acidic enough for healthy azaleas or rhododendrons.

I see too that your climate in summer can be hot and humid, neither of those are favorable to growing azaleas in containers - if you experience hot humid weather you may need to consider containerizing these plants as purely experimental. Special attention must be paid to aeration of the container mixture or roots will decline from the fungus that thrive in warm damp conditions. For best results you should try for a coarse textured material with air space between the particles - here, bark chips and perlite mix would be recommended, I don't know what is comparable that is available to you. Both are nutritionally inert so you would have to supply regular fertilizer. Also, planting in large containers is said to improve the heat/moisture conditions often found in smaller containers.

This is not chlorosis. Chlorosis has green veins and yellowing between the green veins. This is yellowing of the leaves. It has several possible causes:

Uniformly yellowish-green leaves is often just the need for more nitrogen. This will be more noticeable in the full sun. Some less sun tolerant varieties will always be light green in full sun. Use a good organic nitrogen like HollyTone at half strength. Do not use chemical nitrogen as it can damage the roots and the mycorrhizae that feed them.

Conversely too much shade will cause the leaves to yellow due to lack of chlorophyl production

Water stress when the leaves are first forming will cause yellowing. Either too much water or not enough water can do this. Wet/dry fluctuations will also do this to new foliage.

Here is a link that might be useful: How to grow Rhododendrons and Azaleas

Thank you so much for the help.. i really appreciate it.. :)

From the points you people raised, what i understand is to take the plant out and see for any root damage, then replant it in a coarser medium.. i can prepare somewhat acidic potting medium with pine needles and bark along with coco chunks and sand.. also i have yellow sulfur which i use in making potting mix of gardenias..

rhodyman, thanks for the great link..

I have a foliar fertilizer which i use on my roses and gardenias, can i use it on my azalea?.. here is the composition in ppm i used for spraying my plants weekly:

Nitrogen-----------900
Potash-------------7.5
Magnesium--------1.5
Zinc--------------4.5
Boron------------1.5
Iron--------------7.5
Copper-----------0.05
Manganese---------0.5
Molybdenum-------0.00001
Cobalt--------------0.00001

Azaleas are not heavy nitrogen feeders, so I would normally say this is not a good mix for azaleas. But since yours apparently needs nitrogen, it should be OK until things start looking better. A nitrogen problem can be caused by a shortage of Magnesium, so that is a good. In fact it would be interesting to apply that first and see if they green up with just Epsom Salts.

Potash and Iron are companion nutrients also and your mix has them.

Your mix doesn't have calcium. Gypsum is a good source of calcium that doesn't raise the pH like lime does, hence gypsum is much better for azaleas.

The boron concerns me. Excess boron can create the same symptoms as fertilizer burn. I would be leery of using that much. I really don't know how much is enough. I do know that perlite that has boron will cause problems. That is why you must always use "horticultural grade" perlite.

I took the plant out and just as expected the roots were brown and rotten... :(

I clipped some, applied some rooting hormone and planted it in plain soil.. i dont have much hope..

Thank you for the help.. :)