The quality of your rock looks questionable, some being lava and the rest I can only assume being made up of lead being that you have 50lbs in a 41 gallons and it looks empty
You might want to consider new rock all together, unless your rock was freshly shipped/uncured then you shouldn't get major algae problems right off the start. I'm guessing it's just a bunch of random rock from another hobbyist, so not only is the wrong stuff but probably polluted as well. Not a great way to start your first tank!