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Back to basics: Light is what determines everything else you do with an aquarium to grow plants and not algae. With a 125 gallon tank, no pressurized CO2, you have no choice but to go with low light and the plants which can do well with low light. Low light, using T5HO bulbs is far less than you now have. I would use half of the light you now have, and that might still be too much, even though some people have had good luck with even more light and no CO2 - those people are very much a rarity.
Plants don't need more than 10 hours of light a day, and 8 hours is really plenty, so I would reduce the lights on period to 8 hours.
Your plants should all do fine with that much light and that light duration, if they get enough nutrients. Enough nutrients means nitrates, phosphates, potassium, trace elements and a source of carbon. I would buy some potassium nitrate, mono potassium phosphate, and either CSM+B trace mix or use Flourish as the trace mix. Those I would dose per the EI method, only because it is very easy to do, but I would only dose about half the amount recommended for that size tank. For carbon, it has to be either pressurized CO2 or Excel. Excel might be adequate if the light level is low enough - very expensive, but adequate. You can buy those fertilizers from http://www.aquariumfertilizer.com/ or http://www.greenleafaquariums.com/aquarium-fertilizer.html and a few other online stores. Excel tends to be cheapest from either BigAls or Drs. Foster & Smith, during their sales, and in 2 liter or bigger jugs.
Last, why are you using RO water? Doing so makes it very hard to do weekly 50% water changes, which you need to do if you use the EI fertilizing method. If you feel you must use RO water, you probably will be happier using the PPS Pro method of fertilizing, both of which are described in the fertilizing forum stickies. If you use RO water you do need to add back the calcium and magnesium you removed - plants need both. You can buy calcium chloride and epsom salts (magnesium sulfate) to do that.
Plants don't need more than 10 hours of light a day, and 8 hours is really plenty, so I would reduce the lights on period to 8 hours.
Your plants should all do fine with that much light and that light duration, if they get enough nutrients. Enough nutrients means nitrates, phosphates, potassium, trace elements and a source of carbon. I would buy some potassium nitrate, mono potassium phosphate, and either CSM+B trace mix or use Flourish as the trace mix. Those I would dose per the EI method, only because it is very easy to do, but I would only dose about half the amount recommended for that size tank. For carbon, it has to be either pressurized CO2 or Excel. Excel might be adequate if the light level is low enough - very expensive, but adequate. You can buy those fertilizers from http://www.aquariumfertilizer.com/ or http://www.greenleafaquariums.com/aquarium-fertilizer.html and a few other online stores. Excel tends to be cheapest from either BigAls or Drs. Foster & Smith, during their sales, and in 2 liter or bigger jugs.
Last, why are you using RO water? Doing so makes it very hard to do weekly 50% water changes, which you need to do if you use the EI fertilizing method. If you feel you must use RO water, you probably will be happier using the PPS Pro method of fertilizing, both of which are described in the fertilizing forum stickies. If you use RO water you do need to add back the calcium and magnesium you removed - plants need both. You can buy calcium chloride and epsom salts (magnesium sulfate) to do that.