We have a 30 gallon long tank, with a variety of fish. We have 2 AFD's, and just recently got 2 Hi Fin Pleco's (please excuse me if I spelled the name wrong). I have noticed the last couple days that if one of the frogs gets under the Pleco to get to a shrimp pellet, as an example, the Pleco will start, how can I put this, it looks like he's doing to his back (the frog) what he does to the glass. I don't know if he is just cleaning off stuff from the frogs back, or if this is a danger to the frog. I was video recording the 2 yesterday with my phone and have on the video the Pleco doing this. Once I realized what I was seeing, I immediately chased the Pleco away. I can upload the video for anyone to see, but for me it's kind of frightening to watch. Oh and this morning, the Pleco was doing this to the other frog. And the frog, after a few seconds wiggles and moves away. They both appear to be fine. I am looking for an experienced owner's advice, and not just guesses. Thank you.