For your tank dimensions, those lights you are using should be okay... i use LED lights with even less power in the same tank size with similar Co2 and fert dosing and my hairgrass carpet (the Tropica sp. mini type) showed noticeable growth within a few weeks.
The main difference i can think is i use ADA Amazonia aquasoil, not H.E.L.P soil, not sure if that makes that big a difference though.
I guess you can try increasing the light intensity by adding a 2nd set (or trying different lights with spectrums designed more specifically for growing plants) and see if it helps. If algae starts becoming too much to handle, then can just adjust/reduce the light and look at other possible solutions.
Just for additional considerations:
Whats your tank's fauna bio-load and feeding amount/routine? The flourish comprehensive fertilizer and tabs are relatively low on nitrogen and phosphate content, so in a tank with low or no bio-load, quite often the plant growth slows down and gets stunted due to lack of macro nutrients, then it may be necessary to dose those fertilizers to supplement the plants nutrition needs.
How are you distributing the Co2 around the tank? Diffuser, atomizer or external reactor? And if diffuser, how is it positioned and what is the flow pattern of the tank circulation.
As for Excel, it is only effective for up to 24 hours (it starts to dissipate and breakdown in the presence of light) so for best results, its recommended to dose it every day, preferably at the start of the photoperiod, rather than just every 3 days.
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