It looks like some of the Ammannia latifolia that I gave you.
I purposely gave you the upper stems since they looked clean. Since this is a pretty robust stem plant that seems not to lose its lower leaves, I have seen the green spot more on the older lower leaves and as you go higher it fades until the highest newer leaves are clean. It seems to take a long time to get heavy but still I don't know how to get rid of it. I have arrested its spread and its getting worse by running the diatom 24/7. If I run the diatom for only 3 days after a water change by the seventh day the algae is back forming on the glass.
I have upped my macros and micronutrients per T. Barr and although it doesn't get worse with the diatom on, it doesn't go away. I have recently replanted the tops to reduce the amount of algae in the tank per T. Barr, but I still don't think thats going to prevent the spores from spreading all over the tank if I turn the diatom off. I think Tom's recommendations will reduce the algae and get it under control but I am still fighting it. I am adding 2 ppm P and .5 ppm Fe twice per week along with other traces and KNO3. I do a 50-80% H20 change once per week and have plenty of circulation in the 125 g tank.
If this algae is normal, then I have to rethink strategy here. How come I don't see it in the other show tanks? Do people just grow the plants fast enough so the algae doesn't show on the new growth, but it is still there?
Kevin, don't put any plants into your new 75 until we talk about this. We may have to try something else like bleach.