GSP, great choice
. Spreads like a weed and can survive thermonuclear attack. Just make sure it doesnt come in contact with stoney coral flesh as it can patch a sting
Purple tipped anemone, danger danger will robinson. Anemones are unfortunately NOT beginner livestock. Their captive success rates are poor and they are widely regarded as one of the most difficult pieces of livestock to care for next to perhaps goniopora or demanding SPS. The resons for the poor success rates are not well known, but much experience in both keeping and loosing them exhists among the hobby. If you can, I would suggest taking it back to your LFS for the time being although very few LFS' I know of will take back an anemone once purchased because they are so hard to keep alive. Since that may not be an option, I hope this helps.
General requirments of anemones:
-Mature tank, 1 year old prefferred, 6 months ABSOLOUTE BARE minimum
-Rock stable water chemistry. No fluctuations in chemical parameters. Any such fluctuations can lead to stress. Stress causes the anemone to expell its zooxanthellae symbionts much faster and more violently than a coral would. If it goes overboard (and they often do), the anemone is left with no symbiotic nutrients that it needs to survive. It slowly starves over a period of months and dies
-high light output. they tend to do better under metal halide lighting or some other source of lots of T5/PC lighting. anecdotal successes under T8s or VHO's exhist, but are few and far between.
-The right spot to land. You unfortunately cant control this. Anemones are picky and will move around the tank until they find a place where the light, substrate (rock, sand, crevasse, whatever), and flow are just right. IF they dont find this, they will keep moving, ultimately get stressed and well like I said, stress is bad for them
-good selection when purchasing. Healthy anemones which still have their zooxanthellae typically have brown tentacle bodies with sometimes colorful tips. 95% of the time, an anemone with a white or opaque body and tentacles has allready expelled its zooxanthellae and likely will not survive in captivity. I'm not sure what yours looks like, but I hope its healthy as I described
-drip acclimation. since water chemistry stability is so important, it makes sense that very slow drip acclimiation is used. again, failure to use drip acclimation can cause an expulsion event.
-fish compatability. dont select lazy fish which lay about the bottom of the tank. gobies and other types which like sleeping in rocks may find themselves unwitting meals to healthy anemones.
I hate having to post things like this and rain on people's prades so to speak, but its probably better you learned their care needs now than 6 months from now when its bleached, whithering away, and its too late to save it. I wish you the best of luck in caring for it if you do decide to do so (or if you're forced to by your LFS). If you are keeping it, post up some pictures and let us know if its found a spot it likes.