If your fish's poop is white or yellow and slimey. Your fish is probably affected with intestinal flagellates. Nematodes could be a secondary cause. If you have a microscope on hand, take the poop that is no older than 5 minutes and look at it through the microscope at 50 to 100X. If the poop contains small worms, ranging in size from 1mm to much smaller, this would involve the larvae of livebearing nematodes. If the poop contains whitish, elongated. flat segments with almos squared off corners and an intrigate inner structure ina chain-like appearance than it is tapeworm and you can control it with a medication or if it is healthy than leave it alone, it may go away. If the poop contain numorous spindle-shaped eggs with pointed ends. This would be from thorney-headed worms. The infection is from isopods or water fleas which carry the larvae of thorney-headed worms. No easy treatment. If the feces contain elongated eggs with champagne-cork-like covers (can only be seen at 200-400X) than it has Capillaria worms. Probably not possible because it only happens in freshwater fish.
If you don't have a microscope you should put it in your qt and wait it out to see if it persists. Good luck