I have a 45 gal. fresh water tank that has been set up for 5+ years. There are 3 tin foil barbs, 4 african cichlids (3 are adult) and 1 fire mouth cichlid. They all get along well. However, when I add any scavengers, cats or plecos, they never last longer than 3-4 months. I always thought most scavengers were hardy. Is the tank too large? Do I need more fish? I would like to add scavengers to keep the tank clean and remove some of the algea. But I haven't found any that last. Any Ideas? Is there a cat or pleco that is hardier?