Fish in an aquarium are known to be prolific eaters and will make quick work of eating algae, leftover food scraps and waste from other animals in their tank environment. Their efficient feeding habits help maintain clean water that reduces algae growth in your aquarium; some even use it as their own personal cleaning crew, quickly disposing of dead fish or debris quickly from your environment.
Although certain fish species engage in coprophagia (the practice of eating their own waste), this action only serves a limited purpose and should not be relied upon to clean a freshwater tank completely. Instead, aquarists should utilize species like goldfish as part of their strategy for keeping freshwater aquariums free of accumulation of waste products.
White or stringy fish poop typically indicates a health issue for your fish, such as digestive disease or infection; or simply because they're not receiving enough nutrition in their diet. Whatever the case may be, it is a good idea to contact your veterinarian immediately in order to begin treatments or antibiotics for these conditions in order to protect future health concerns.
Snails and shrimp often mistake fish feces for unconsumed food and may accidentally ingest it, only later to quickly expel it again. By making use of such opportunistic feeders to reduce ammonia levels in an aquarium and reduce frequent gravel vacuuming needs.