Growth has stopped

I am looking for some advice.  

I planted E. tennellus in my 55, and true to form it took off and made a
very attractive carpet in the foreground.  About a month ago, growth
stopped and now many of the leaves are transparent.  Nothing has changed
that I am aware of - weekly water changes 10-20%, lights on a timer
12H/day, 2 40W bulbs 1 full spectrum and 1 warm spectrum (they are about
5 mo. old), temp 78F, pH 7.2, inconsistent addition of FerroVit, regular
gravel no addition to substrate.  Any suggestions to stop the trend and
get back to growth and runners?

Also, in this tank is some Val spiralis which did the same thing (sent
runners all over and stopped).  I had been pruning the Val back to under
the water surface on a weekly basis.  The last time I pruned the Val I
cut it back about 3" under the surface, and it has stopped growing
completely.  Did I stress the plants too much?

There are 2 Crypt wendtii that appear to be fine and 4 E. paniculatus
that have been holding their own with slow growth but lately the leaves
are begining to yellow.  And finally, I have developed a problem with a
thread algae (it has strands 6" or longer in some instances).  The tank
only has 4 fish (2 pearl gouramis and 2 cardinal tetras).  I feed the
fish once or twice a week and only a very small amount.

I this is quite a bit, but I'm just about ready to tear the mess down
and start over.  I really don't want to do this.  Can anyone shed some
light on my problems and get me past this?

Thanks for your help