Tolumnias do best mounted. If you need to have it in a pot, chunks of charcoal are a better choice than PrimeAgra. They need to dry out completely, and the PrimeAgra will probably hold more moisture than the plant needs.
I was discussing Tol. care with Gayla at Carter and Holmes recently, and she said her "new" watering routine is: mist the leaves every other day or so, 1-2x/mo spray leaves with water then a weak mix of Peter's 15-5-15 cal-Mag and flush the pot only 1x/mo. I ended up bringing 3 home and they were all beauties, so I'm trying this routine.
I agree P/A would probably keep them too wet. Mounting, from what I've seen, seems to work really well too.
If it's at all possible for you to mount them, I believe they really do better that way, based on what I've read and on my own experience. Without exception, all of mine just took off when I attached them to small pieces of cork. They had multiple spikes for their last bloom, and all are now putting out at least two new growths each. I spray/mist them daily with distilled water, and add weak MSU to the water twice a week. Just my