[ChadKruger]

From the Marineland manual, it's shows a PAR
Value of [email protected] a 12" distance,same as in my
setup, my ground cover HC grows well up against
The front glass,but is yellowing towards the center.
I also am starting to have thread algae problems in
that area.I'm going to back the fixture off 2", and see if it helps.

I am no expert but from what I've personally experienced is you're have a nutrient deficiency. With that much light you need to do a solid EI dosing. The thread alage sometimes comes from plants leaching out nutrients when they are dying.
You didn't say what your substrate was. Is it inert? Ecoplus?