Seba anomone (help please)

[fishguyxd]

I have one but there are places on it where the tips and tenticle are very small like it has withdrawn on itself or it got burned meaning by salt directly (but that never happened at all) and the middle is very open and exsposed
it's stays in one place, but looks like part of it is trying to dye off there are two clowns hosting in it also water movement is good and water tests are ok ph was 8.0 and now 8.3 no ammonia,nitrite,just some nitrate but I have did water change calcium is 400

So any ideas what could be causing this I am abit stumped

please and thanks