Add a Reflector and perhaps a nice bulb like a Triton.
That should help.
Adding CO2 can help a great deal also even at this level of lighting and DIY should do it.
It will increase the growth and the types of plants you can grow.
Perhaps 80% of the plants out there you can grow pretty well.
Dose fertilizer once a week should do it if you have a good substrate.
I had some very nice tanks with this amount of lighting etc and many nice plants.
Regards,
Tom Barr