There is more to this than simply having a shorter photoperiod. With the benefit of the information from the other thread, [here:
http://www.aquariacentral.com/forums/showthread.php?278163-New-questions ] there is a water and nutrient issue that also affects the Wisteria.
The GH of aparker2005's water is 25 ppm, which is just over 1 dGH. This means that the "hard" minerals, primarily calcium and magnesium, are basically missing. Liquid fertilizers, the best ones that are complete in including all nutrients (except carbon, hydrogen and oxygen) do not have sufficient hard minerals to suffice; these are intended as basic comprehensive supplements and most areas in NA have sufficient hard minerals in the water. Those of us with very soft water (my GH is under 1 dGH) will not have much luck with very fast growing plants such as Wisteria unless we also supplement the hard minerals. I do this in my three larger tanks because my large Echinodorus swords will not manage without the calcium. But in the other tanks I don't, and stay with plants that manage without the supplement. You mentioned in the other thread that Wisteria failed; I believe this was partly due to the hard mineral deficiency, and perhaps light though I don't know which fixture you were then using.
Carbon is another issue with high light. Diffusion is the best way to supplement CO2. I know many use the liquid carbon supplements like Excel and CO2 Booster, but these are toxic and I prefer not adding such chemicals to my fish tanks. Even at recommended doses, these will usually melt plants like Vallisneria, and if overdosed can kill bacteria, plants and fish. Glutaraldehyde (the only ingredient with water) is a strong disinfectant used in hospitals, anti-freeze, embalming fluid...you get the idea.
The photoperiod can only go so far. Plants require a fairly specific balance of light intensity and nutrients in order to photosynthesize. Different plant species have different requirements for both light and nutrients, but these must be in balance at whatever level needed. If not, algae will take advantage. So if the light is too little, extending the photoperiod is not going to make up for this; similarly, if the light is too intense, shortening the photoperiod will not compensate. There is obviously a middle are where this can work, but it is limited.
I have tried a dual-tube 48-inch T5 6700K HO tubes over my 5-foot tank (115g), and it was very bright light. I do not use diffused CO2, as my setups are all low-tech or natural, so after a week this went back and I returned to a dual T8 setup.
Byron.
