| Sea Sun,
Sphagnum is not a strange medium at all. It is very commonly used in a variety of ways for a number of plants. Whether it is the best medium our your plant in your particular growing conditions is another question. I typically grow Cattleya Alliance plants in medium to large size bark with perilite and charcoal.
I always repotted my Cattleyas after they finished blooming while the plant was in its rest period but Cynthia likes to wait until the new shoots and roots appear. I think it's a matter of personal taste and seeing which approach your plants respond best to.
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