That light should give you about 40 PAR at the substrate, low medium light. That defines the plants' growth rates. You need to be dosing enough of everything the plants need so they are not stunted from a lack of any nutrient. It is also enough light that you really should dose Excel, too. Seachem's dosing chart is, I think, intended for relatively low light tanks, so a good starting point would be to dose per that dosing chart, but it wouldn't do any harm to double the dosages until the plants are growing well. Then you could drop the dosage of one of the nutrients at a time, and observe the plants for a few days to see if the growth rate, the appearance of good health, or any pearling are reduced. If so, you shouldn't reduce the dosages. If you see no adverse effect, you can again reduce the dosage a little bit and again observe the plants for the same adverse effects. Repeat until you see an adverse effect, the raise the dosage back to where there was none. Then do each of the other nutrients the same way. Or, just stay with 1 1/2 to 2X the dosages in the chart, but replace about half the tank's water every week or so.