I've had good luck with peppermints too. I had to buy two of them though. The first one did nothing but when I added another it didn't take long to get rid of my aptaisia. I did some looking into why I needed two peppermints and I found that depending on where the shrimp came from determines whether or not it will eat aptaisia. I also found some info saying that they prefer to be in groups.
HTH
Nice tank BTW
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