Home Depot or Lowe's carries Moss Out which is a chemical that will rid you of the moss. Use a straw broom and use it going side to side not downwards since it will remove the moss faster and easier. Hmmm best way to describe is gable to gable.
I used that Round up on mine. Spray it on and let it sit for 30 minutes or so then use a straw broom to clean it off. It worked really well and I haven't had any problems since.
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Tide with bleach works too! Oh yeah a good preventative is to lay copper wire on the roof.. don't know why it works but recommended by a good friend who is a roofer add a comment
Not to be obvious but the best way to go to get moss off 3 tab roofing is to prevent it from happening in the first place lol. Seriously though I learned the hard way to never use a pressure washer to clean it. Look for cleaners made for this.