It's like a crap shoot with perculas hosting an anemone. Some won't host an anemone for over a year, some will host an anemone as soon as you put one in your tank. When I had mine, they would sleep at the top of my water line. Then started to host a hammer and frogspawn coral that I had in the tank for a few months. Took them over a week to start to host a RBTA that I put into the tank. I think though that in due time, they will eventually host an anemone. Now I am looking at your current tank setup, and I don't think an 18g tank is big enough for an anemone. I could be wrong, but mine is pretty much taking over my 75. That is unless you don't plan on having anything else in your tank other than that anemone.