After six months of setting up this 215 gallon freshwater aquarium we are
still experiencing green water and some thread algae - altho the thread
algae is very minimal now. Here are the stats:

Acrylic Aquarium 6' x 24" wide x 30" high

Iron - 0.1 ppm
pH - 7.0
Ammonia - 0 ppm
Nitrite - 0 ppm
Nitrate - 2 mg/l (by Profi-Test)
Nitrate - 10 mg/l (by AquaVital Multi-Stick)
KH - 10 degrees
Total Hardness - 120 ppm (AquaLab-1 Stick)
Total Alkalinity - 300 ppm (AquaLab-1 Stick)
Phosphate - 0.03 mg/l (by Profi-Test)

Fish Load is as follows:
8 med/lg angel fish
11 glowlight tetra
8 silver hatchets
4 neon rainbows
3 rainbows (2 red new guinea, 1 turquoise)
3 small plecos
3 cory catfish

Plant Load:
17 " from right side is giant vallisneria (trim each weekend)
24 " from left side is giant vallisneria (trim each weekend)
(Vallisneria is thickly planted from front-back on each side)
3 very large profuse java ferns on driftwood
4 med/lg cryptocoryne wendtii
1 large bronze cryptocorne
4 red mellon swords (large)
3 large amazon swords
Small number of pygmy chain swords
1 bunch of scarlet hygrophilia

We do have substrate fertilizer, and we add 21 mls daily of PMDD minus the
potassium nitrate which we add separately to try to get the nitrate up to
10 - 15 ppm.
We also have a pH meter attached with the CO2 cylinder with reactor to keep
the pH at 7.0 (would be 8.2 if left without CO2).

Lights - we have power compacts 4 x 96 watt daylight bulbs which figures to
2 watts per gallon. Could it be there aren't enough watts/gallon?

The plants are growing nicely and spreading, but the green water won't seem
to go away and now there is a little thread fuzzies on the Vallisneria and
cryptocorynes again. We change at minimum 50 gallons of water/week.

Any thoughts on why the green water???