Why Does My Guppy Have White Stringy Poop? (Answered!)

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There can be multiple causes of white stringy poop in guppies. Internal parasites are the most likely cause, but constipation and poor water parameters are also common causes. Identifying the cause of the white stringy poop is the first step to solving the problem.

Guppies have long been one of the most popular fish in the freshwater aquarium hobby. They are colorful, friendly, hardy, and generally easy to care for. I got my first tank of guppies over 30 years ago, and I have been keeping and breeding guppies ever since.

Most people will find they keep guppies for years with very few problems. Occasionally however you may notice a guppy that has white, stringy poop.

What Causes White Stringy Poop In Guppies

There are a number of different factors that may cause white stringy poop in your guppies. These include;

  • Internal Parasites
  • Constipation
  • Lack of food
  • Poor water quality
  • Stress

Treating Internal Parasites In Guppies

Internal parasites are probably the most likely cause of stringy white poop in guppies. Guppies are true scavengers. They will eat anything and everything. Guppies can often be seen eating from the bottom of the aquarium and typically this is where they consume either the parasites themselves or their eggs.

Guppies often pick up internal parasites either when they are at the wholesalers or in the fish store. By the time you get your new guppies home, the parasites are living in the guppy’s intestines and consuming much of the goodness from the food the guppies eat.

Fortunately, treating guppies for internal parasites is relatively easy these days. There are a number of products on the market that will quickly treat your guppies. Paracleanse by Fritz is probably one of the best on the market (check the current price on Amazon HERE)

Constipation In Guppies

Guppies can become constipated when they have a poor diet. Low-quality foods have lots of fillers in them. Fillers offer the fish no nutritional value, they are only added to bulk out the food.

Preventing constipation in guppies is easy, you just have to feed them a balanced diet. A good quality food like Bug Bites from Fluval contains all the nutrients and fiber a guppy needs to keep its internal systems running properly. Adding live or frozen foods to your guppy’s diet brings in yet more vitamins and minerals.

If you find your guppy is constipated, feeding live or frozen daphnia or brine shrimp can help. The shells of the daphnia and brine shrimp act like a natural laxative to the guppies. Just one or two feedings can help ‘unblock’ your guppies intestines.

Lack Of Food

White stringy poop in guppies can sometimes be a result of guppies not eating for a while. If your guppies are new to you and you see white stringy poop, try offering them some good quality food or some live or frozen bloodworms.

If your guppy eats the food, give it a couple of hours and check their poop again. If the color of the poop roughly matches the color of the food they just ate, the chances are you have solved the problem.

Poor Water Quality

Poor water quality can occasionally lead to a guppy having white stringy poop. An ammonia spike or high levels of nitrates in the water can have a major effect on your guppies health. White stringy poop from your guppy could be a sign something is wrong with your aquarium water.

If you suspect your water quality may have become poor, carry out a large water change (maybe 30% to 50%). Bringing in freshwater should help redress the water quality balance.


Stress can take a toll on your guppies. If their aquarium is overcrowded, if water quality has dropped or maybe the guppy is being bullied by another fish, the result could be white stringy poop.

If you have tried some of the suggestions above, but your guppy still has white stringy poop, look at the fish’s environment and see if stress could be a factor. If you can discover the source of the stress and deal with it, your guppy will probably start to have normal poop again fairly quickly.

How To Avoid Guppies Getting White Stringy Poop

There are a few things you can do to prevent your guppies from getting white stringy poop in the first place.

Quarantine New Fish

Quarantining new fish before adding them to your aquarium is the first line of defense when it comes to preventing fish from spreading internal parasites. By quarantining your new fish (keeping them in a separate tank for 1-3 weeks before adding them to your main aquarium), you have a chance to treat them for any internal parasites or diseases they may be carrying.

You also have a chance to observe them before introducing them to your existing fish. Prevention is much better than cure when it comes to fish parasites and diseases.

Regular Aquarium Maintenance

By carrying out regular water changes and gravel vacuuming your aquarium substrate you reduce the chances of any internal parasites spreading or your water quality dropping to an unacceptable level.

Carrying out aquarium maintenance also gives you the perfect opportunity to stop and observe your fish. Spotting a problem early, and dealing with it, may prevent the problem from becoming a major issue.

Avoid over or underfeeding

Underfeeding or overfeeding your aquarium can cause your guppies to have white stringy poop. Set up a regular feeding schedule and feed good quality foods to keep your guppy’s internal systems running as they should.

In Conclusion

If you discover your guppy has white stringy poop, take some time to work out why. If the fish is new to you, or you have recently added other fish to the aquarium, the problem may be internal parasites.

White stringy poop doesn’t mean it is the end for your guppies. Whatever the cause, there is a good chance you can solve the problem and nurse your guppy back to full health.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James