Thanks guys for your pointers!

My HM takes up about 30% of my tank, which is about the same amount as my Elatine triandra. My HM does shows healthly and lush growth, but its growth rate is nothing compares to my Elatine triandra, Rotala wallichii, Ludwigia brevipes, Riccia fluitans, Rotala sp. green and Rotala indica. In fact all the plants in my scape are exhibiting healthy growth with zero signs of any nutrient deficiency, except for a small percentage of my HM.

Let me give a better explaination of the symptons on my HM. It happens only to a small percentage of my HM, and only on the top 2" of the plant . The leaves that are affected are actually well developed and not just the shoots at the tip. It seems that before it melts away, the color on the center tissue of the leaves are very light green in color. The stems on the top 2" of the plant are also affected as well.

My old lighting setup is decent, but aparently not enough to supply light to the both ends of my tank, which results in very very slow growth to my plants in those places. And those plants happen to be high light requirement plants. In fact my new HQI setup is giving all my plants even healthier growth than before. Not only they are showing more vigour and lush, they are also becoming more compact. Where else they are more leggy under my old lighting setup. The only setup back is more heat coming from my chiller with more frequent kick-in.

For now I'm doubling my phosphate in each dosage, and instead of dosing everything 3 times a week, I increased to 6 times a week.

Will update you guys later. Many thanks again!