I’m having trouble figuring out what this thing is, a couple of them came on a clump of spaghetti algae I had purchased. I will post some pictures down below. Sometimes I will notice them swimming through the water column like a jelly fish when I shut off the pumps for couple minutes to feed my seahorses. These organisms are so tiny, when I was feeding live baby brine shrimp in the tank once, I noticed one these organisms touch a bbs and it paralyzed or killed it. From a side profile of the organism, they look like tiny clear octopi.
