I had at least 100 aiptasia in my Reefer XL 425 over a period of several months. They were on rocks, on the sand, in my sump, refugium, and probably in my overflow but I didn't bother to check there. At first I used a laser to zap them, which was fun and gratifying, but I couldn't get a direct line of sight on several that were behind rocks or corals. Over time I realized the laser would never be able to fully rid the tank of aiptasia.
On Feb 12 I put 10 berghia nudibranchs in my tank. They immediately went into hiding in the rocks and I didn't see them for weeks. I also didn't see any improvement in my aiptasia infestation. Then one night I managed to see a nudibranch crawling around the rocks and it was about 10 times larger than when I first added them.
Again, it quickly went into a hole in the rock and disappeared, but at least I knew they were alive and growing. After about 2 months I realized there were far fewer aiptasia, and several that had been annoying me that I couldn't hit with the laser were gone. After 3 months, I can't find a single aiptasia anywhere in my tank, sump, or refugium. They have been completely eradicated by the nudibranchs. I feel bad for the nudibranchs because they have probably starved to death, but they completed their mission admirably.
I highly recommend berghia nudibranchs, but just keep in mind you need to have patience as they quietly work on eating the aiptasia at night. You'll rarely ever see them, but over time you'll see the improvement.
