Man, I hate that I missed out on this discussion while I was gone!
I think you guys are on track. Make small adjustments to the CO2, raising it a small amount at a time to see how the fish and plants respond. I've got as much light as you, though, and only have DIY CO2 (resulting in 6-10ppm) and I don't have the hair algae problems you describe.
While raising CO2 levels might get your plants to pearl, to get them to really grow, you need to leave those macronutrients in your water. I use PhosZorb myself, but only occasionally, when phosphate levels get out of control (more than 1.0ppm) due to disturbing a Jobe's stick in the substrate, or a dirty filter or an old piece of driftwood.
The biggest evidence of nutrient starvation is that Amazon Swords. Those things are pigs. If your Nitrates are below 5ppm, they will do horribly. I try to keep mine actually above 10ppm by adding KNO3 (stump remover) weekly.
Those Dupla Tabs are great, and will keep that substrate enriched. Your substrate is getting better with time, not worse. Jobe's sticks will provide even more potassium and much needed Nitrates to those root feeders. It will supply some phosphate as well, but you don't want to get rid of all of it. Let the plants do their job.
You've got a good understanding of higher order plants competing for nutrients against lower algae, you've just got to let it develop into practice in your tank! When nutrient levels drop, plants will suffer. Algae can survive and even thrive in amazingly low nutrient levels. Eliminating nutrients is a bad way to get rid of algae.
Get those good low range NO3 and PO4 test kits, raise CO2 in small increments every few days, and try some low Phosphate fertilizer sticks to get those Swords happy. Good Luck!
- Sam P -
plantedtanker in limbo - all tanks currently in storage