LEAVE IT ALONE!
Sorry to "Shout" but I cant stress this enough....seriously, dont feed it, dont do anything else to it for several weeks.
Couple of things:
1...why did you move the anemone? If its not moving, leave it alone. These animals will move on their own to reach their preferred location in the tank. Often, this is not where we would like them to go. They can and will move on their own, that is one major reason why Anthony Calfo and others are strongly against keeping anemone's in tanks with corals
2...if you're going to keep an anemone in a tank, you need to keep in mind they will move to where they want, and they dont have eyes or a brain, so powerheads, pump intakes or impellors are not something they see as a threat. You will need to cover them up, or find a way to make them inaccessible to the anemone to prevent what happened to yours. Also keep in mind, they can and do move by inflating with water, releasing their hold, and drifting with the current, which can blow them into powerheads, pump intakes and impellors...Ive had it happen to me before, so I know what I'm talking about.
3...If your anemone gets stuck on a pump/powerhead or impellor, DONT REMOVE IT! Turn off the pump, and allow the anemone to work itself free. This is much less stressfull and damaging to the anemone. Let them get themselves out, and you stand a better chance at saving the anemone. Seriously.
4...When anemones get stressed, (like after being sucked into something), they will expell their Zooxanthellae, (the photosynthetic algae inside them that gives them color), which is why they look white. This also happens when they are shipped. The term for this is bleached. Your anemone is currently bleached out. It still has some zoox inside it, but it is very white. White is not a natural color for anemones.
5...Feeding your anemone after being shredded can actually cause more stress on the anemone. I dont know why, but I can tell you from experiance that it happens. Best bet is to let it recuperate for a few weeks, and then try feeding it small amounts. If it accepts the food, then feed it three times weekly, (again in small amounts...too much food will either stress the anemone or the undigested bits will get spit out...making a nasty mess to be cleaned out by you later.)
6...after a shredding like yours, if possible, try to keep clowns out of the anemone until it heals up. They can also be a stress on the anemone.
Just to give you some background on where my information comes from....
I've been keeping anemones for about 7 years now. I currently have 4.
(1) Heteractis magnifica that I've had for almost 3 years
(1) Heteractis magnifica that I've had for 3 months. Two weeks after I got it, it wandered into a pump, and severely shredded. The shredded tentacles released their nematocysts into the water column, killing all my fish except my clown fish. Its still allive, and I've been working very hard at nursing it back to health. I fed it 3 days after it got injured, and it promptly expelled most of its zoox, nearly killing it. It just yesterday ate something substantial w/o expelling more zoox....I think may have turned the corner and will be able to get it back to full health.
(1) Heteractis crispa that I've had for almost a year and has trippled in size.
(1) LTA, (M.doreensis) that I've had for about 6 months.
I am by no means an expert, and certainly dont want to come off as one, but I do have experiance with anemones....
For more information on keeping anemones, you can click on the link in my signature which will take you to the RF Resource Library. Look in the invertebrate section, and you will find several articles on anemones....
Nick