by Carl Blakeman

Pothos (Epipremnum aureum) does not release chemicals; instead, they absorb and break down harmful airborne chemicals and toxins from the air. The primary airborne pollutants pothos is documented to neutralize include:
Formaldehyde
Benzene
Toluene
Xylene

In addition to air purification, pothos roots are exceptional at absorbing dissolved chemicals and heavy metals from water, making them popular natural filtration systems for aquariums. However, the plant itself contains calcium oxalate crystals in its sap. If ingested by pets or humans, this can cause chemical irritation to the mouth, tongue, nd digestive tract.

Calcium oxalate crystals are highly insoluble in water, meaning they do not dissolve into the aquarium water under normal, healthy pH levels. Because of this, pothos roots growing inside a tank are perfectly safe. However, calcium oxalate is a physical irritant rather than a chemical poison, and it can become harmful to fish under specific onditions:

  1. Ingestion by Herbivorous Fish
    The crystals are shaped like microscopic needles (called raphides). If herbivorous or curious fish—such as goldfish, silver dollars, or certain cichlids—nibble on submerged pothos leaves or stems, they ingest these crystals. The Damage: Once inside the fish’s highly acidic digestive tract, the crystals begin to react. They can tear at the delicate lining of the fish's mouth, throat, and stomach, causing severe internal irritation, swelling, or an inability to eat.
  2. Physical Irritation from Fresh Cuttings
    If you take a fresh cutting from a pothos plant and immediately place the raw, severed stem directly into a small aquarium, a small amount of sap can ooze out before the wound heals over. The Damage: In tight or low-volume aquarium systems, these free-floating needle crystals can contact the fish’s external mucous membranes. This can cause slime coat degradation and skin or gill irritation as the fish swims through the water.
  3. Decaying Plant Tissue in the Water
    If a pothos leaf submerges, dies, and begins to rot inside the tank, its cellular structure breaks down.

The Damage: As the leaves disintegrate, they can release these microscopic raphides into the water column. Free-floating needle crystals can scratch the fish's body, damage their protective slime coat, or irritate their sensitive gills.

How to Safely Use Pothos with Fish
You can easily prevent calcium oxalate harm by following a few simple safety rules: Submerge roots only: Keep all leaves and stems completely out of the water. Only let the clean root system sit in the tank to absorb nitrates. Let cuttings heal first: If propagating pothos, let the cut end of the stem air-dry and callous over for 24 to 48 hours before putting it in the aquarium. Prune dying leaves: Promptly remove any yellowing or decaying leaves before they fall into the water and break down.

Pothos has great powers; use them wisely to have long-lasting success in your aquariums.