I think the black jungle guys use an almost 100% cypress mulch mix so they water often and don't have to worry about the mix breaking down or having a build up of salts.
You may be better off trying an organic fertilizer if you use Sphagnum Moss. In my experience, osmocote made the LFS decay very quickly.
With Neptune's Harvest theres only a small problem with algae and moss (not sphagnum) growth, the Live Sphagnum actually seems to enjoy this fertilizer too.