Jacquie, I am no expert here, particularly when it comes to tillandsia. Tillandsia are like any other bromeliad, losing lower leaves as they age and when they go semi-dormant. So those lower leaves don't cause me any alarm. I have a feeling that unless you mount your tillandsia (like I do all of mine), they don't have a way to grow roots. Root growth is simply a way for them to attach to whatever porous material they might be mounted on, just like they do in nature, growing in trees. I have 8-10 varieties mounted on that large slab of cork, and some varieties show root growth and some show little if any. Roots can be awfully fine though, the size of a human hair. The yellowing orchid leaves are perhaps older leaves. If you are seeing new growth, particularly this time of year, your orchid is probably doing fine. Have you noticed any new root growth? Many orchid varieties will be semi-dormant this time of year, and yellowing leaves will begin to be evident. Only when my orchid is a semi-deciduous or deciduous grower, and fall/winter is its dormant period, will I withhold water. Sometimes I will mist the plants occasionally, but some plants won't even get a misting. Without leaves, with few leaves, and in dormancy, the need for water is reduced.
That being said, I would water your plants more often. Your orchid is nothing like a deciduous grower. The orchid is growing in a mesh-pot, and the media would thus dry out more quickly than if growing in solid plastic. I love mesh-pots, believing that this is closer to how they grow in nature, with air movement over the roots and media. Solid plastic does afford them this air-movement but it does hold water longer. The tillandsia have no media/pots whatsoever, so these plants dry really fast, particularly in our heated homes during the fall and winter months. There is not much humidity in our homes. In my opinion, misting every few days would help raise that humidity around individual plants. I would water all your air plants (remember, orchids, staghorn ferns, "typical" bromeliads, and tillandsia are all air-plants) at least weekly, unless they don't look dry (they all should).
In my opinion, Tillandsia fertilizer and orchid fertilizer can be interchangeably used on all your plants. These fertilizers for the most part are very similar to our "regular" water-soluble fertilizers, but should have some micronutrients that are beneficial to air-plants. I basically never quit fertilization unless the plant gets no watering. I do reduce my ratio of 1 tsp. per gallon to 1/2-1/4 tsp. per gallon in the fall and winter months.
