I've tried everything except Berghia to get rid of Aiptasia over last two decades. They will always come back over time. Slowly at first and then depending on tank conditions rapidly spread into a horrible outbreak.
If you have visible aiptasia in DT/Overlow/Sump you most likely have many more tiny/invisible Aipatasia everywhere else. If you tackle your DT by carving them out or rocks, scaping, or treating with chemicals they will eventually come back since they will seed from other places you can't treat.
Copperbands have worked for me to control Aipatasia in DT but they don't take care of the rest of your system (Sump, overflow, etc). Copperbands are difficult fish, and even more difficult to keep alive for the long term. One of my favorite fish, but sad to see them die a year or two later. Some folks are lucky to keep copperbands long term.
I've tried pepermint shrimps. Can't say they work. It's a hit and miss, plus other concerns about them going rogue.
Chemical treatments, scrubbing, typically aggravates the Aipatasia and they spread more. Sometime more rapidly.
The only way I've managed to completly get rid of Aiptasia is Berghia Nudibranch. They are not alway availble and certainly not cheap. You don't need many. Actually don't get too many since Berghia eat nothing but Aiptasia and they die of stavation when there is no more Aiptasia to eat.
Beghia seem to work slow at first however I think at the early stage the Berghia's are eatting the tiny aiptasia in crevaces, in and under rocks, so you won't see them. I actually thought the beghia I added died or got eatten. After a while you'll notice aiptasia dissapearing everywhere. In a few months you won't have any Aiptasia anymore. Berghia are delicate creatures and if you get small ones they can't handle strong flow, so they won't be able to get to the aiptasia in high flow overflows (I think) so treat those area's as mentions by other above. You may have to add or move the Berghia's into your sump after your DT is cleaned up.
I introduce 5 small Berghia into a 30 Gallon tank 3 months ago. Dozens of Aiptasia. Last week not a single Aiptasia left. The big Berghia's started coming out and crawling on Glass since they were hungry and would starve very soon. The Berghia grew up nice and big. I caught 4/5 and 2 Beghia's have been move into my 90 Gallon tank that's infested with Aiptasia. I put 1 berghia into my 110Gallon Tank that have a handful of Aiptasia, and left one in the 30 Gallon just in case there are any Aiptasia remaining.