Just my 2 cents - Your po4 level is pretty high compared to your no3. I know the 'golden ratio' is 10:1 (no3 to po4). It may be that your po4 may be driving your iron too low? Personally, I would try increasing no3 and decrease the po4. Something to like 10ppm no3 and 1ppm po4. I've always had success with S. Repens @ those levels in my tanks. BTW - I realize that you have some red stem plants and may be purposely low dosing no3 to bring out the red.