Red cherry shrimp. It's a quarantine tank, too. My last purchase was about 3 years ago, Kuhli loaches from Aquahuna, and they all got along great.The aquarium co op sponge filters are a really nice product. Wish they'd ship internationally. After running my aquaeon (i believe) sponge filter for about two years (actually it might be more than that), I can definitely say that the small details Cory prides himself in adding to the filter really help. I could barely fit my airstone inside the filter. The base itself wouldn't sink unless the sponge sunk. The fine sponge also isn't the greatest. Not so noticeable with a small bioload, but it definitely helps. What's your stocking on your 5.5?