I prefer injecting them with kalkwasser. You're not using enough to effect the water any, and on top of that, you're adding just a small amount of calcium back in to the tank.
Unfortunately, I haven't found a biological solution for the problem that I like. Peppermint Shrimp are hit and miss, various Butterflyfish are also hit and miss and even a little finicky (not to mention expensive), Berghia Nudibranchs seem like the ultimate solution but I don't want to have an animal that will starve to death when the food supply runs out. I don't want to have money in my tank just die off, nor do I want to have an animal that is doomed in my tank.
With all that said, there is one other option that I can only confirm 50% but my wife confirms 100%. We had a Molly Miller Blenny (Scartella cristata) --RIP We miss you!-- that I've heard stories of them eating Aiptasia. I've never seen them do it, but my wife says she has. I'm inclined to believe her since we used to have Aiptasia in that tank but they disappeared. I couldn't confirm if it was the blenny eating them or if it was my persistance in kalk injections. I'll let you make the judge. Oh, and if you do find a Molly Miller Blenny on the market, PLEASE LET ME KNOW! I've been searching for one for a long time and would jump on it in a heartbeat.