Small BTA anemone like this isn't going to "nuke my tank" even if it died and decomposed in the tank, so I would not worry about this. (even in a 16 gal biocube)
Most important for him to recover is having adequate flow. Leave him in stagnant flow and you will ensure his demise. He does look a little stressed but nothing BTA cannot recover from. More important is how he got here in the first place. You need to make sure the tank water is good and stable and then try to situate it so that he goes not get detached and sail right into the overflow box or PH.
Using something like a strawberry basket, or even build a box with common egg-crate and zip-tide to keep him in there and not blown into the PH.
Good luck with him
Most important for him to recover is having adequate flow. Leave him in stagnant flow and you will ensure his demise. He does look a little stressed but nothing BTA cannot recover from. More important is how he got here in the first place. You need to make sure the tank water is good and stable and then try to situate it so that he goes not get detached and sail right into the overflow box or PH.
Using something like a strawberry basket, or even build a box with common egg-crate and zip-tide to keep him in there and not blown into the PH.
Good luck with him