A ten gallon is enough for a single T. biocellatus. A pair for a 20. A pair of T. nigroviridis (or fluviatilis) needs a 29. They really don't need much in the way of interaction. In fact, they generally hate other fishes. At best, they ignore them. At worst, they eat them. Your C. travancoricus might not be eating for several reasons. What have you been trying to feed it? They generally prefer to eat live foods or frozen foods. Try frozen brine shrimp, frozen blood worms, and frozen mysis shrimp, and if you can get your hands on a baby snail, try that too.