Aptasia is a nuisance anemone that comes on live rock. While you’re at the LFS, see if they have some AptasiaX. That will take care of it. If you can, take all the livestock back and ask them to hold it for you. While there, ask if they have test kits other than API. They are notoriously inaccurate. I recommend Red Sea or Salifert. When you get home, shut off the lights and let the tank finish the cycle. By turning off the lights, you’ll put a dent in the algae. If what’s on your sand is red, it’s Cyanobacteria and will likely resolve itself. To help identify the algae, go to reefcleaners.org and read their info. If you can get the livestock out, you don’t need to do a water change. Just let it finish. Test periodically. Keep us updated! This is a great time to collect up any supplies you might need. Bulk Reef Supply has a great video series called “52 weeks of reefing.” You can find it on their website or YouTube. Feel free to ask any questions you have....
And welcome to the reef!