Fungus in Your Fish Tank? Could Be a Good Thing.

Posted by Augusta Hosmer on

Read Time: 4 minutes

Okay, sure, the title sounds kinda clickbait-ish. Most people hear "fungus" and think either "athlete's foot" or "mushroom," but what if we told you fungi might help you grow aquarium plants

Mycorrhizae: Pretty Fly for Fungi

Land plants have a well-documented symbiotic (mutually helpful) relationship between their roots and a huge range of fungal species naturally found in soil called mycorrhizae. Mycorrhizae actually translates from Greek to "fungal root." The fungi infects the plant's roots, obtains "food" (carbohydrates) from the plant and, in return,  increases the plant's root absorption and nutrient uptake by increasing root surface area with small, thin structures called hyphae (pieces/filaments of the mycelium, which is sort of like a fungus root system). 
This relationship has a ton of benefits for most species:
  • Plants can absorb previously unusable/insoluble essential nutrients
  • Can reduce transplant shock
  • Helps maintain soil structure 
  • Some data suggests it can alter soil pH
  • Protects plants from stress/some illnesses/drought
  • Potentially improves seed germination
Mycorrhizae in Soil
To show you how widespread and important it is, it's currently estimated that over 90% of land plant species have mycorrhizal relationships. 
Funny enough, even though us fish tank people are interested in this for our aquarium plants, one of the prevailing theories for how some plants transitioned from fully aquatic lives to dry land millions of years ago is through these mycorrhizae. Go figure.

Mycorrhizae for Aquariums

There's not a lot of research on this relationship for aquarium plants specifically. Most of the publications I could find are actually just from the past decade (seems like a long time, but in science, that's nothing). That said, the TLDR for now is this: based on the evidence we do have, it looks like mycorrhizae are useful in aquatic plants. 
Originally, scientists believed it was only land plants that could benefit from mycorrhizal symbiosis, but there's emerging research that suggests even fully submersed plants have mycorrhizal relationships. Several surveys of fungal populations on aquatic plant roots have been conducted across the world and yep, you guessed it: mycorrhizae are there. How much aquatic plants rely on them compared to land species is up for debate at the moment - if I find new studies, I'll be sure to edit this and link them. 
Lots of folks also mistakenly believed you couldn't add mycorrhizae to fish tanks because the fungi would just drown. Turns out, several mycorrhizal species appear to work with or without oxygen based on a 2020 experiment with them in aerobic (with oxygen) and anaerobic (without oxygen) aquatic conditions in rice paddies. If you're interested in the study, check it out at this link! 

Should I Add Mycorrhizae to My Planted Tank? 

It depends. If you're on a limited budget; happy with how your plants look; and/or growing hardy, beginner aquarium There are probably better ways to spend your money (even though these aren't typically super expensive). It's fun to spoil our plants and you might see some benefits, but it's not something you need to worry about if you're just enjoying planted tanks casually as a hobbyist. Your fish certainly won't care either way. 
Lots of companies are good at advertising it like it's a must-have or your plants will die, of course, but think about it: one of the main advantages to mycorrhizae is absorbing nutrients, especially if they're scarce. In a tank environment where we overfertilize, etc. and don't have huge areas of soil to maintain and modify, they're less crucial. 
If you have heavy feeders or easily stressed plants, like to experiment, or really want to push your plants and/or see how this might benefit more challenging plant species, there's no harm in adding it. There is a lot of anecdotal evidence from folks who have used it with positive results and taken their tank to the next level, but you can definitely grow aquarium plants without it.
One other application for supplementing mycorrhizae in aquariums is with biotope tanks, depending on how specifically you want to replicate the environment you're capturing. If you have a soil profile for the region, you could mimic it in your tank down to the beneficial fungal species present if you wanted. That seems a little extreme to me, but I've probably done weirder in the name of being an aquarium nerd. So, to each their own.

How to Add Mycorrhizae to Your Aquarium

Most aquarium mycorrhizae for sale comes in two forms: either a mix of species in a separate supplement (often powder, granules, or liquid) to add to your substrate or already built into one (like a premium planted tank substrate or dirt/soil). It's sometimes called an "inoculant" if you're shopping for it. A lot of them will come with beneficial bacteria species, too. Just follow the packaging instructions. Typically, they'll tell you to add liquid and gel supplements directly to the water column and other types around the plants in the substrate.

Three brands of Mycorrhizae

Also seen some stories of shoving pill capsules filled with mycorrhizae powder into the substrate. Or, you could do something like a root dip before you add your plants. Whatever works for you. 

Just like with bacteria/bioload, once you get a colony going, you don't need to keep adding more mycorrhizae continuously. Just maintain them unless you make large modifications that could kill the fungus. Some fertilizers don't interact well with it.

Also, when using any kind of fungal supplement, be careful about breathing it in when you use it.

Can I Use Too Much? Is It Safe to Use with Fish, Invertebrates, Ponds, and Aquaponic Setups? 

If you're following dosing instructions, you should be fine. That said, it's not likely to cause problems if you accidentally use too much. It's 100% safe in aquaponics/hydroponics - you eat food grown thanks to mycorrhizae already. It's also hard to find info on how safe it is for specific fish or tank/pond environments, but it is unlikely to cause harm given its presence in natural waterways. Just double check for other ingredients in your mycorrhizal supplement to make sure there's nothing harmful to aquatic organisms. Should be on the safety sheet. There are actually some fungal supplements made specifically for hydroponic setups and aquariums, if you're interested and want to be sure.

Hit us with post suggestions and comments, and tank on! 

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