Adding live sand and/or removing a bit of rock, or changing pieces of rock can help you for your aquascape... It look like you've put 40 pounds in your 20g :p
For my build I've took 2-3 bigger pieces and the rest is small piece... It look like this
A sand bed (optionnal in your case because you have a lot of LR
) will help increase the eye appealing of your tank IMO
A blue background can give a good effect, in my case I decided to not put a background.
For the lighting, the color spectrum is Ok, but the output power is not so strong. I have 60w led
power on my 20g. For this lighting, I'll recommand you never add high light corals, they will suffer from poor lighting. Focus on low light species, maybe it will work.
Your nitrates are a bit high, are you using RODI
water ? Or maybe your tap contains nitrates ? Do a 50% WC
before you add livestock, will drop your nitrates 50% if your tap is clean or if u use RODI
wata. Anyway, you have a low light setup, so nitrates will probably not be a problem for algae invasion. In my case, If nitrate raise to just a little trace of them, I have algae problems because of highlight.