Just to eliminate certain questions, do this for a couple weeks Ken, 50% water change instead of 25%... or at least
a third of your water and then change the water flow in the tank.
there was no movement at all at the bottom third of the tank
I have always found that the best water flow is at the bottom of a tank... not only because of the substrate freshening but also because it takes the nutrient pockets that can emit from the substrate and pushes everything up to be filtered and moved. Also, most
of the slower growing plants that we keep will really flourish with good water flow over the rhyzome... if these plants rhyzomes recieve fresh "moving" water the entire plant will respond better. Older growth on these plants survive, stay healthy looking , but becomes "stagnant" if you will and become a target for algae. In nature that leaf would just die off but in our aquariums we tend to push them past that "natural" state.
You said that you have no spot on the glass.... the reason I am thinking that the spot algae is not on your glass is due to the current water circulation.
Where do your powerheads point ? Along the glass ?
If that is the case, you will get a "whirlpool effect" around your tank that you think isnt bad, but it will in effect create a large dead spot in the center of our tank where most of our plants tend to be.
Also , the more foliage we have, the less circuation there is... powerheads need to be adjusted in location or even added to a tank to compensate for growth.
Back to nutrients... What are you supplying the micro's with , Flourish also ?
With regards to iron, I seem to have a problem with this. I does Floursih twice per week and I underdose it.
One more thing... dose your Iron per the bottle
...it says 5ml per 200L... do not dose a smidgeon under that for now !You dont want to know what I dose for Iron in my tanks... I will tell you it is more then that in higher watts :shock:
Hey Ken I could have sworn that I saw photos of your tank at one time but I cant seem to find them... that would really help in trying to solve this...
But for grins and giggles, try water flow at the bottom of the tank and a couple weeks of bigger water changes... Just a thing like "fresher water and better circulation " may take care of your problem...