Nice sphagnum! I doubt you'll deplete your sphagnum supply since he stuff will just keep growing and growing. If you want to start up a new culture just trim the sphagnum heads off of a nice tall culture and put them in another holding tub. They will most likely be replaced with off shoots, so it's no worry .
Nice update! I bet it's pretty hot up where you live today... had to activate the doghouse AC unit an hour earlier for the Neps :|. 50 degree night temps? Nice! What are your day temps now with that cooler in there? I'd say the coffee treatment has taken its effect on the rapid fire sphag and the huge Nepenthes leaves from the last update .