I was wondering whether or not it is safe to add any type of play sand ontop
I did this, but the first time you vacuum the substrate, the sand will sink to the bottom and the bigger particles will move to the top.
Changing/adding sand won't kill the algae.
What/how often do you feed?
How long do you run your lights?
What are your water params?
If you have aiptasia, they are nasty little critters and can overtake your tank. I have no experience with them so you might want to ask others that have.
Just to make sure they are aiptasia can you get a pick. I wouldn't want you killing off something that is beneficial.