I have to question if it is Alger or is the sphag growing ?
as regards to too much light one has to try to picture where sphagnum moss is grown
it loves filtered light I have seen it growing on rocks that get covered with snow in winter ( I have even been stupid enough to try and get fresh sphag in winter.. yep you guessed it frozen solid )
here we go I just found these sites
DPIW - Sphagnum Moss - Sustainable Use and Management What Is Sphagnum Moss? Parks & Wildlife Service - Sphagnum Moss Sphagnum and Water http://www.fpa.tas.gov.au/fileadmin/...6_Sphagnum.pdf
I hope this post helps