Yellow streak at end of Phalaenopsis leaf

[ELORCHID]

I noticed that a couple of my Phals have developed a yellow streak at the end of their leaves, not sure whether its a cultural problem or virus. I've attached a photo of one of the leaves. This particular plant was repotted (in a bark mix) about three months ago after it finished flowering and is currently developing new buds, I'm watering every 7-10 days with tap water and fertilizing every 3 of 4 watering, its also sitting Approx. 1.5 feet from the window. Thanks in advance for all your help.
Sorry for the picture quality but it was taken with a 3.2 megapixel Kodak EasyShare camera.