Hmmm no one has replied so I'll throw my 2c in.

What do you normally do for sanitation? What's your CYA level? Why consider a algecide? Do often have Algae problems?

I would add floaters and leave the cover on, and fix what happens when you get back.

The cover should reduce CL loss due to the sun so maybe you're CL will be high when you get back!

You should check your CYA when you get back, but I doubt 2-3 weeks will raise it that much.

Robert