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Poison Pothos!

One topic that will no doubt be raised when considering using terrestrial plants in aquariums, and rightfully so, is the toxicity of certain plants and their utility in an aquarium. In particular, pothos is thought to be toxic to some animals.


But in truth, nearly ALL Epipremnum/riparian plants, even monstera, peace lilies, anthurium, all have this same 'toxin' throughout the entire plant, leaves and roots. The 'toxin' is Calcium Oxalate. It's not actually toxic to fish due to its insolubility in water with a pH that supports fish. It requires a very acidic environment to leach into the water as it becomes soluble at <=pH 4.5. Above 4.5 it's remains crystalline, which is the actual issue for dogs and cats as the crystals can cause irritation or sores in mammals.


But even if it manifested any toxicity, if your pH is above 4.5, it cannot leach into the water as it's insoluble.

Significant solubility doesn't occur until the PH is under 3.5.

Should you harbor any doubts or concerns about using terrestrial plants due to this issue, you can actually test for the toxin yourself with simple, home urinalysis test strips such as the one below. These are calibrated in mmol's such that conversion to PPM would be required had we needed an absolute value, but we don't need one.

Below is a Home Urinalysis Test Strip. This indicates how much oxalate is present in urine and is used to determine the risk of kidney stone development.

Oxalates, as indicated above, cannot leach into water without additional energy being applied. If the water pH is 4.5 or lower, there are free electrons suppling this energy. Since this is far from the pH in most tanks (the test tank is pH=8), we made a 'tea' using heat energy to drive the oxalate from the pothos leaves (left). If ANY oxalate leached, the strips would develop some blue color. If no change, the oxalate stayed in the plants:


QuantiQuik Oxalate Quick Test Strips (10 Strips): Industrial & Scientific


The test aquarium was a 125 gallon, overstocked cichlid tank with four, large pothos plants. These have been growing out of the tank for approximately three years. If the tank's pH was indeed low enough to dissolve the Calcium Oxalate crystals in the plants, Calcium Oxalate becomes Oxalic Acid when dissolved in water which ironically is not toxic at all.  In fact, if you've ever given your fish any fresh greens, in particular dark greens like spinach, you gave them oxalates. 

Anecdotally, for what it's worth, the LFS owners who facilitated the test below, have actually not seen an incident of toxicity with Epipremnum/riparian plants in any of their aquariums nor their customers. You may read the results of the original test here:

Alternative Nitrate Reduction via Emergents - Photos, Videos & Journals - C.A.R.E. (aquariumcoop.com)

In brief, there is no toxicity issue in using most terrestrial plants in freshwater aquariums.




Edited by dasaltemelosguy
Added Oxalate Test Evidence
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I love posts you make like this. Thank you.  I use pothos in every tank. I have never had issues but it’s good to know definitively it is safe. Thanks to your Alternative nitrate reduction post I was inspired and picked up some lucky bamboo for me tank 😁


Edited by Guppysnail
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  • 1 year later...

Going off of that, it probably isn’t a good idea to have Java fern with herbivores (commonly it is suggested to have Java fern with things like silver dollars because that is one plant that they won’t eat) because (at least for scat) it is toxic, more research is required but just watch out!

On 11/13/2021 at 10:09 PM, OnlyGenusCaps said:

Don't get too excited there.  Fluorescence not bioluminescence.  More like GloFish than glowing mushrooms:

THE LIFE NEUROTIC WITH STEVE'S ISSUES - among ... But wouldn't that be cool too?!

Speaking on bioluminescence, did you know in the saltwater hobby you can get flash light fish! Now that would be a cool aquarium!

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