disgusted with persistant algae

[RMoore7167 at aol_com]

I've about had it. 1 year and I still cant get it right. You all have been 
great in supporting me. So let me try this again. Ive tried a few things and 
nothing seems to help.  Im getting algae on the glass (very fine light green 
scum plus a little green spot) I went on vacation for a week and a half and 
now all my plants have a thick dark green mat of algae that rubs off pretty 
easily.  Here are my specs.

55 gal tall
fish loading            have 4 tetras, 2 gouramis, 1 angel, 4 ottos, 5 algae 
eaters and 2 yoyo loaches 
water change        every week 50%. i do notice alot of demitrus from fish 
CO2 injection       with Tom Barrs Ber2
lights-                 151 watts   Photo period was at 14 hrs to 12 to 10 
now just changed to 9hour/day. It in a fairly dark corner.
uv light sterilizer -   Ive tried constant running and only when change 
water....no difference
hot magnum filter-  I was told to take charcoal out and substitute small 
gravel instead. No difference with or without charcoal
                    could the hot magnum not be turning water over enough?
PH-                 6.5 in a.m to 7.0 in p.m
temp-               82 deg
kh-                 3.5 to 4.0
phoshate-           0.0 Is there different types of tests that test organic 
vs inorganic. (or does it matter) I was told that I should have at least some 
in water (i've tested tap and                   aquarium) Im using a seatest
ammonia         0.0
Nitrite             0.0
Nitrate             10-20ppm. With no fertilization
FE                  unknown
Potassium           unknown

As far as fertilization goes I've experimented alot.  I have always added a 
10 drops of a PMDD (CSM plus epsom salts).  Lately experimented with the 
addition of liquid Iron.  I have also played with increasing doses of 
Potassium nitrate started with 1/4 tsp every other day up to 1/2 tsp.  I 
thought things were getting better but when I did Nitrate test I was over 
60ppm so stopped. was getting good pearling (not that this means that much) I 
was also adding 1/2 tsp of Potassuim sulfate once a week. Never saw any 
difference. Just to let you know I have done this in about a 6 months time.  
When I was fertilizing alot everything was growing crazy.

I even turned off lights for 3-4 days and covered aquarium to see if I could 
eliminate problem

What am I missing here.  Im about ready to through in towel. But invested so 
much time an $ I really hate too. Plus the comments when it is clean make me 
want to keep.