Algae, though no PO4 or NO3

[Leslie Wheeler <leslie_wheeler at verizon.net>]

I've been a lurker on the APD list for about 4 years, since setting up 
my first planted tank.  The advice and references from you folks has 
been great!

My first tank was a 38 gallon tank, low light no CO2.  It did pretty 
well for over 3 years, but finally plants just stopped growing (i had 
midget hygro, midget vals, everything midget) and BGA started to happen. 
 I crhronically had high PO4 and pretty high NO3 readings in that tank 
as well.

I recently "upgraded" to a 65 gallon setup,  36x18x25, 110W CF lighting, 
CO2 via 2 of those new Hagen kits (~DIY).  mix of flourite and natural 
gravel substrate with some fertilizer pellets down deep.  Eheim 2260 
filter (i LOVE this filter -- very very quiet).  Plant growth seems to 
be fast, esp vals which are taking over; swords having babies, etc. 
But algae is also a problem:  first it was black brush along the edges, 
now it is the green carpet fuzz on a lot of things, esp leaves higher up 
near the lights.

Plants:  various swords, vals, Anubias nana, bacopa, cabomba (which has 
no algae on it), hydrocotyle, water wisteria.

I do have a fairly high fish load, mostly small tetras and cories, a few 
angels.  10 ottos.  No snails thanks to a clown loach which I really 
should trade in; he's gotten a bit too big.  I feed only once/day, if 
that.  Fish seem healthy and happy :)

I do supplement with Flourish, Flourish Iron, Potassium, a few times a 
week.  I have been adding some extra Flourish Excel just to see whether 
that woud help.  Somewhat to my surprise, with all of these fish, no 
measurable PO4 or NO3.  pH also is high -- it appears over 7, and on my 
old tank, i regularly was in the 6.5 range.

I don't really understand why the algae is so prevalent, given the lack 
of P04 and No3.  So I'm not sure whether I should ADD something, or try 
to TAKE AWAY something.

Suggestions much appreciated --

Leslie, in Pittsburgh PA
where May seemed more like April, weather wise, this year...