Resurrecting this old thread because I have something new to add to it and it may help folks in the future with this issue.
I too, had this problem and googled everything I could find to try and get rid of them... It would have been fine if it was just a couple of them, but their population exploded and they covered everything. Squishing was to no avail. There were just too many. It looked like my tank had a bad case of acne. As it was only a 40G Breeder, loaches were out of the question.
I tried everything I could think of, *outside* of the tank. I set up another 10G and put a sample of all the plants I had in my main tank in it and nucked that tank with everything I could think of... First I simply tried Ace Hardware Ammonia at about 1.5ppm. Kept it at that lever for a week and a half. THEY LIVED THROUGH IT!!!!!
Plan #2: Tetra Algaecide. For 3 weeks. They just laughed. I think I even saw one waving a tiny limpet middle finger at me...
Plan #3: Copper. Therapeutic levels for 2 weeks. Die you little bast@&%ds! Die! Die! Die!!!
Plan #4: No Planaria. Made the water totally gross. They just threw a party. And didn't invite me. I was so depressed.
Plan #5: Desperation. Ammonia at 1.5 ppm, copper at therapeutic levels and Tetra Algaecide all at the same time - for a full month. Finally!!!! Success!!! Death to Limpets!! Death to them all!!!! I threw a party... and I didn't invite any limpets.
But yeah, okay. So I probably couldn't do that to my main tank. So I decided to use the 'sterilized' plants from the 10G test tank, bleach everything else, new substrate and start again. Sigh.
But I was saving up for a rimless, and figured I'd have it in a month or two, so I put it off. While I was waiting, I added a 6 pack of cute little otos. A week later I happened to walk by the tank - and stopped dead in my tracks. OMG - I could see through the glass.... Where were all the limpets???
I love my little otos ♪♫♪♫ I love my little otos ♫♪♫♪ I love my little otos ♪♫♪♫!!!!! They're acting just like tiny little loaches, and the limpets seem to be perfectly oto-sized! I still see a limpet here and there, and when I do I squish. But I so rarely see them anymore that I'm fine with it.
Did I mention that I love my little otos?
Hope this helps someone else!