Hi Matt,
Well, Barr might have possibly been talking about Non-CO2 tanks for low flow. I can't quite remember the thread but some time ago he came to the realization that even with EI dosing people were still experiencing a lot of algae issues, primarily CO2 related, so he started emphasizing nutrient delivery via flow. What we do know is that there is a preponderance of evidence that there is a night and day difference between low flow and high flow in highly lit tanks, and that the tank is way more forgiving and efficient at higher flows. The higher the flow, the more forgiving. Another thing that people don't realize is that as the plants grow it becomes more and more difficult to deliver nutrients/CO2 due to blockage so the 10X rule helps you down the road even if it seems a bit high at first.
Uptake by the plant leaf is attenuated by a thin boundary layer between the leaf surface and the water column. This layer of zero or low velocity water is referred to as "The Prandtl Layer" and occurs at the interface of all surfaces making contact with fluids in motion. The velocity very near the leaf surface slows due to friction. In plants this boundary layer is a problem because the uptake mechanism is via osmosis from a more concentrated nutrient area (the water column) to a less concentrated area (the leaf's aqueous solution). The thicker the layer, the more isolated the water column's nutrients are since the leaf uses the nutrients within the layer first, then nutrients must diffuse from the water column into the layer and then to the leaf. Higher flow reduces the thickness of the boundary layer and in a way force feeds the leaf by constantly refreshing the layer with new nutrient supply.
Additionally, if there is detritus on or near the leaf (which constantly occurs) and if this detritus decays, then you have NH4 buildup at the leaf surface. The leaf will uptake some NH4 but in the presence of high light algae are adept at sensing and responding to the NH4 loading rate. High flow helps to rid the leaf surface of waste and detritus to minimize this threat.
Based on this, my feeling is that in fact, poor filtration exacerbates the other problems in the tank and should be considered a high priority instead of an afterthought. You will often see where filters are suggested for certain tank sizes by the vendors or by the manufacturers, but for high light tanks these ratings are totally meaningless.
George has pretty good luck with TPN+ but his water is already high in nitrate and phosphate so it's often very difficult to zoom in on the right dosages for another persons water area. From a cost standpoint EI dosing will bring better value. JamesC tested ammonia and urea dosing for a while. You can see the interesting discussion in this thread:=>
viewtopic.php?f=11&t=925
Cheers,