Mysterious fin flapping

[FSM]

I have recently noticed some odd behavior in my green terror. He occasionally rapidly flaps his pelvic fins back and forth against his underside, basically "clamping" the fins and then unclamping them rapidly and repeatedly. It lasts a few seconds and I have only seen him do it a few times. Is this cause for concern? He has exhibited no other behaviors except this, and is active and appears healthy. Not some bizarre disease, I hope.

I read through the sticky about diseases, and didn't see any that include this as a symptom.

 

[2004exrider]

Keep an eye on him for a while. He may be on the first stage of ggetting ich. Have you done anything new to the tank recently that could have changed water conditions?

Jimmy

 

[FSM]

I noticed it maybe a week ago, and saw him do it for the first time again today. I replaced the sand yesterday.

 

[navygirl76]

you replaced your substrate? could your tank be going through a mini cycle? id check your water parameters (ammonia, nitrite and nitrates) and see if something is going on there..

 

[FSM]

I will check them, but I noticed the behavior before changing the substrate, which doesn't make sense if the new sand is the cause.