Having some problems with my 40 gallon right now. Filtration is a Marineland penguin filter good for 70 gallons. Substrate is sand and the only decorations are a plastic tree type thing, a floating turtle dock, and a slate rock. I started off with just a baby slider/cooter type turtle and a baby Alligator Snapper (both around 2 1/2 inches shell length). A week ago I stocked the tank with some minnows and goldfish as feeders. On Friday I decided to get some tankmates so I picked up a medium-sized pleco, one adult electric blue acara, one small blood parrot cichlid, and a two and a half inch peacock cichlid. In the morning, I found that the acara had VANISHED. Not under the slate rock or inside the plastic tree decoration, not in the filter (the pipe has a piece on the end of it that stops fish from being sucked up), and he was far too large for the turtles to have eaten him and for there to be NOT A SINGLE TRACE LEFT. I assumed he had jumped out the space on the back of the tank overnight and he had flopped out onto the floor and my dog had eaten him, because I looked everywhere and there was no body. But TODAY, now the peacock cichlid is nowhere to be found!!! My dog has not been inside at all, and it's the same situation! I'm stumped and I'm scared to buy any more fish until I figure out what's going on. Can anyone help?