H.Sebae is probably the hardest to keep anemone to get and according to what ive read not even the professional aquariums are managing to keep them alive longer than a year.
And also be careful not to confuse H.magnifica to H.crispa
Im an anemone guy and ive tryed these couple of times and they always die in few weeks/months ive kept Haddonis that are easy compared to Malu white anemone.
Malu should stay in the sea.btw some of these large carpets and Sebaes can be over ten's or hundreds of years old and its a really sad think to rip them out of the sea just so they can disolve in your aquarium.
I think you are confusing a bunch of anemones with each other here.
First, a H. sebae does not exist.
Second, Heteractis crispa (Leathery Anemone) and Heteractis magifica (Magnificent or Ritteri Anemone) are hardly to confuse with each other, not just by looks, coloring and the texture of their tissue but also by behavior - H. magnifica will always try to go to the highest spot in the tank and often end up on the front pane of the tank.
H. magnifica is due to this behavior and bacterial infections one of the most difficult anemones to keep alive in an aquarium.
I think H. malu is the anemone that usually is called Sebae anemone despite not being a natural host for A. sebae (neither is H. crispa). H. malu is very easily confused with H. crispa as a small crispa or one in bad shape can look almost identical to a malu, right down to the color and the purple tips.
H. crispa, if not totally bleached, and colored back up can be very hardy. I kept one for several years in the mid 80s. Back then I was lucky that my bleached crispa picked up some Zooxanthellae from a neighboring anthelia colony and fully regained it's color and then tripled in size. The one I have right now is completely bleached and hasn't regained any color within 3 months. Due to that it started shrinking and I'm not sure if I can still turn it around.
The problem with crispas is that they arrive to 90% bleached at stores.
Even worse, often they bleached already at the exporter and some of those then find it a good idea to dye them in yellow, red or any other color of the rainbow. Any of those is most certainly doomed.