I have had my Red-Finned Shark for two-weeks. She is in a ten gallon tank with three Marble Lyre-fin Mollies(two male, one female), two ghost shrimp, and two Bamboo Shrimp. About a week ago one of my bamboo shrimp died. I found out that my filter was too powerful for bamboo shrimp but not before the other died a few days later. Since then my Red-fin has been acting strange. She started swimming and floating around sideways at first. Now she has stopped eating and is showing the signs of oxygen starvation; however, none of the mollies are acting this way. My mollies and ghost shrimp seem to be fine. I have two lava sculptures, a large cave, three small live grass plants, and a small fern plant. My red-fin is obviously stressed due to her color fading to pale grey around her head and mid-body. What is the problem with my Red-fin and how can I make her better?
Your tank is too small for a Red Fin Shark aka Rainbow Shark, it needs at least a 30 gallon tank. Your tank is also overcrowded. You also would need a 30 gallon tank for the current fish and shrimp you have. I would consider moving these fish into a larger tank or you will likely lose most of them.
To immediately help your Red Fin Shark, do a 30% water change and change the carbon in your filter. Do another 10% water change in a couple of days and test your water parameters. Then do 25% water changes weekly. You could also add an airstone if you don't currently have one. You MUST do 25% water changes every week. In this case where the tank is overcrowded, I would do 25% water changes on the weekend, then another 10% water change about mid week. Change the carbon in your filter once a month.
Here are a couple of links to help you with your Red fin Shark.
Please consider moving these fish into a larger tank so they will be happy and healthy. Hope this helps, good luck!