Most likely it is not a fertilizer issue, Nancy. Sounds like a light issue to me. Nine times out of ten when an orchid is large and mature enough to bloom and it is not, it is because it is getting insufficient light. Try increasing the amount of light your orchids get. Also, you note that she is growing in a bark mix. Her orchids might have better air exchange in their root systems too. This could account for the longevity of her orchid blooms. Repot one or two of your orchids into a bark mix and see what happens in 6 months or so. I would expect a marked improvement. In any case, with sphag, you need to repot every 1.5 to two years because of the amount of decay and how the moss will hold fertilizer salts. Good luck.