Congrats! You have a very robust plant! Bifr. thyrianthina is a estrictly rupiculous species, founded in southeastern Brazil (when I live). They love much light, and can live under full sun; I think your specimen has a too dark green color, and it will appreciate more light (a bit more than cattleyas). The roots of Bifr thyrianthina will rot if they are continously moisted, so use a good draining material (more or less 1/3 of the pot) like carcoal pieces and clay pellets, and a easy-drying media (I use an ad-mixture of tree-fern fiber, coconut chips, bark and carcoal). Spots on leaves are normal, and is normal the falling of leaves in back pbulbs as well. Bifrenarias love organic plant food in their roots, I use 'bokashi' (powdered fish among other stinking stuff), and I think Atlas Fish Emulsion would be a good choice. Aditional chemichal fertilizer misted on leaves (Peters 20-20-20), biweekly, low doses (0,5g per liter), helps too bloom. Thyrianthina is the bigger Bifrenaria species, and is an easy grower and easy blooming. Some big specimens of Bifr harrisoniae that grows on rocks (harrisoniae is facultatively rupiculous) are confounded with thyrianthina; some experts says that a great number of cultivated 'thyrianthinas' are in fact 'harrisoniaes'; the differences are quite clear: the harrisoniae spikes are short (often shorter than the pbulbs height), and the spurs in the flowers are short as well. The thyrianthina spikes are long (often as height as leaves) and the flowers spurs are long (its former name were Bifr. magnicalcarata, ie, with a very long spur). Both have a great number of color varieties. Take a look in my gallery!
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Frederico
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