Tranformer question and bleach comment

Sorry for starting the bleach war.  I still cannot understand why, if it's
possible to do, I shouldn't try to keep my 75g brush-algae free.   Worrying
about what these algae would do to the average home aquarium (well, that
and laziness) is what keeps me from giving away or selling all that plant
matter I hack out every week or two.

New Topic.  I am "rolling my own" UGH cables, power supply, and controller.
I read somewhere that I need to find a transformer that does not have the
primary and secondary windings wound together.  Where on earth would I find
such a thing (or do I have to roll my own transformer too)?

TIA, Dirk