I have a 150 gal. heavily planted tank, fertilized with CO2 and PMDD.  Nitrates are 5-6 ppm, Fe is 0.5 mg/ml, GH = 120-130 ppm, Ph is 6.4-6.6, phosphate level is below 0.1ppm.  The weird thing is every time I do a water change I suddenly see a burst of activity in my plants, i.e. the plants release oxygen bubbles like crazy.  This, to me, indicates a nutrient deficiency but I can't figure out what it could be.   Any idea's???

Scott Corbeil