Yep, me too. It seems to be happening with the current tank I have. I've got a plecostamus that has gone months at a time without being spotted. Though lately I see him a lot more. And this past week I bought four clown loaches. Two of them were doing great, swimming about entertainingly. The other two seemed to have vanished. I looked everywhere. Got down on my hands and knees and looked on the ground. The tank is next to the kids' toy box, so i rifled through that too. Got out the flashlight and looked under the radiator. Nowhere to be seen. So yesterday I started rearranging some plants, and like magic, I've got four again. Yeah.