Hi and welcome,
The Dwarf Hair Grass looks to me like it wants more light. I may be totally wrong. Some plants need more light anyway. I guess my only advice is to bring your plant encyclopedia with you when you shop for plants and make sure your plants don't need major lights. That's just me, though.
If it's not too unsightly, I would leave the allgae-infested rock in because if the algae get's worse, you know something is out of wack, sort of like an indicator of how your water is.
"I use API Co2 booster/Aqueon plant food/FlorinMulti to dose my tank. I am wondering are these fine?"
I've heard that FlorinMulti is good, and that all Co2 boosters are bad because of the chemical they contain.
I can recommend Seachem Flourish Comprehensive as I use it and Flourish Root Tabs for those heavy root feeders. I hope things work out as well as possible for your tank.