This is my first saltwater fish. I added him on 2-9-19. The tank has him, 1 hermit crab, 1 peppermint shrimp, and 1 feather duster. The tank is 9 weeks into cycling. The last water test on 2-9-19 came back 0 ppm for ammonia, nitrite and nitrate. Hes been eating well and has been super active. He hasn't done this since I took the video. The water temp was a little high (82) so I turned the heater down. I added a power head yesterday and did a 10 gallon water change on wednesday. Salinity is 1.024 and has been stable. No corals currently. And when I do the water changes I use the siphon and have siphoned all accessible sand areas. Any ideas as to why he did this?