1 vanda dormant? another green tip burn

[rcheng]

Hi,
I have 2 air vanda, a yellow and purple. The yellow vanda was growing well with 2nd bloom, 2 weeks after the last bloom dried and drop off. There were >30 green tip air roots. About 2 weeks ago, the green tips roots began to stop and became white instead, when i switched to soaking the vanda with rain water for 4 hours almost daily like what i did with chlorine free tap water. Then, i switched back to soaking it in tap water which was kept for 1 night to allow chlorine to evaporate. After 1 week i noticed 1 or 2 roots became green tips only. i think the vanda is in dormant state. Appreciate advices?
The purple vanda was growing slowly soaking with chlorine free tap water and fertiliser, like the yellow vanda. After weeks, many green tips appeared. >30. However, about 1 or 2 weeks ago I noticed that 1 and then 4 or 5 green tips began drying and then became black. Appreciate help to let me know what went wrong?