About two more months and I can claim I've had my H. magnifica six years.
To me the ingredients of a succesful long-term husbandry are:
(Ranked in terms of importance, but don't get me wrong, ALL are important)
1) aquascaping and placement
2) current
3) lighting
Most of which you can probably surmise by observing where you are most likely to find them in the wild, i.e., in shallower waters usually, at the top of the reef, where currents and lighting is strongest.
1) Aquascaping and placement.
IME they like to be at the top of the reef. If they can "sense" a way to move higher, they will. I.e., so placement in a tank needs to be as far away from any higher surfaces as possible, including the glass walls. If they can touch a solid surface higher than they are, that's where they're going to go.
In a tank the best thing to do, IMO, is create a "coral bommie" which is a tower type structure with a flat surface on the top for them to be. In your photo, it looks like you have one to the left there, although I think the top looks a little too jagged for optimum placement, I think they'll like a smoother surface. In my tank I used a pizza sized slab of live rock that was pretty flat.
2) Water currents
At the top of the reef the water currents tend to be strong and surging. A wavemaker device of some kind is thus ideal, or a surge tank, or something. I use 2 Tunzes on a multicontroller to get a current that alternates in direction every 10 to 15 seconds. A wash of current from the left, a wash of current from the right. I also have my sump returns piped through a Calfo-style manifold that direct currents from all corners of the tank towards the anemone.
3) Lighting
Again it makes sense that they like lighting but I find that what's more important is that they can sense that they are as close to the light as possible, as opposed to a specific wattage. I kept mine for many years under 2x175W's and now still only a single 250W. But the trick is to place the coral bommie directly underneath a light. This will help "root" the anemone in place.
To further emphasize my point, in my previous tank where I had this anemone, I had 2x175W halides, one on each side of the tank with the anemone directly under one of them. A couple times I had troubles with one of my halides starting (ie. wouldn't start right away, took as long as 20-30 minutes to turn on). One time the light above the anemone was the one that didn't start, and within that half-hour before it turned on, the anemone moved towards the side of the tank where the light was on. "Oh, the sun is over there now." Luckily the same phenomenon worked in my favour when I got the light working again, all I had to do was turn off the light on the side I didn't want the anemone, and it eventually wandered back to where he was before.
...
One warning, be prepared for this species. First of all, getting one to survive might be tricky. And if you do get one that lives, they grow to a large size, will wipe out corals if they get enough contact, can kill off an entire tank's fish stock if disturbed enough to get into a defensive posture, and need a large energy input (ie. lighting and feeding), and will put a tremendous load on a tank's bioload. I've not had a single tank with this anemone that didn't suffer chronically high nitrates. Right now the tank mine is in has a NO3 level of about 30 and I can't reduce it beyond this, so unfortunately until I can upgrade the skimmer or change things around, I can't keep corals in this tank (what's the point, they'll just die in conditions like that).
Not the greatest picture of the setup mine is in, but here's a picture anyhow:
