guppy grass

Guppy Grass: The Perfect No-Maintenance Plant

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Guppy grass, najas grass, or – scientifically – Najas guadalupensis, is a fast-growing plant that removes heavy metals, toxins, ammonianitrite, and nitrates from the water while producing oxygen. It consumes almost every free nutrient in the tank – giving little opportunity for algae growth.

Although the name implies that it’s best for guppies, shrimp also love clinging to it as it has tons of nooks and crannies to pick food off of and hide within. Most small fish will also use it as a spawning mop, such as ember tetras, neon tetras, celestial pearl danios, and rainbowfish. It provides cover for the newly hatched fry and gives them a continuous source of microscopic food, such as infusoria.

If you’re considering adding guppy grass to your tank, read on to learn more about what it needs and some of the most common pitfalls!

Guppy grass species card


Yes, guppy grass needs light to grow. If you want a plant that doesn’t need light, look into hornwort. Guppy grass will become greener the more light you give it, but will start to yellow under lights that are too bright. 

It grows incredibly fast. While there are no studies available citing the growth rates, it grows quickly enough to overrun your tank in a few weeks – if not sooner. This is especially true in highly stocked tanks, such as guppy breeding colony tanks.

Yes, goldfish are notorious for munching down on najas grass. This might be useful if – though more likely when – you find yourself overrun with it if you have goldfish. Aside from goldfish, I don’t know of any fish that will eat this plant, if you know of some, let me know!

Guppy Grass Overview

Difficulty: Easy – although disposal may become an issue
Size: 3’+ (almost a meter)
Propagation: Side shoots, clippings, and vertical growth
Fertilizer: Liquid
Speed of growth: Quickly
Temperature: 50 – 86F (10 – 30C)

pH: 6.0 – 7.0 – though likely higher
Hardness: 2 – 25 dKH
Placement: Floating, planted, or weighed down with plant weights
Origin: Americas
Aquascaping: Floating
Availability: Very common

Difficulty: Easy – although disposal may become an issue
Size: 3’+ (almost a meter)
Propagation: Side shoots, clippings, and vertical growth
Fertilizer: Liquid
Speed of growth: Quickly
Temperature: 50 – 86F (10 – 30C)
pH: 6.0 – 7.0 – though likely higher
Hardness: 2 – 25 dKH
Placement: Floating, planted, or weighed down with plant weights
Origin: Americas
Aquascaping: Floating
Availability: Very common

Guppy Grass Care

Najas grass inhabits a variety of areas in the wild – from fast-moving rivers to stagnant ponds, freshwater to brackish, and temperatures ranging from 50 – 86F (10 – 30C.) Salinity levels under 8 ppt (or 8,000 ppm) seem to be an acceptable range, but it may be able to go higher. There’s almost no tank or waterway that it can’t inhabit. Does that mean that every situation is ideal? Eh, probably not.

Ideal conditions look like a pH of 6.0 – 7.0 with a dKH anywhere from 2 – 25 – though the temperature seems to matter very little when it comes to its happiness. In lower flow situations, it does seem to grow better and fragment less, leaving less of a mess for you (and your filter!) to clean. Similarly, lighting doesn’t seem to matter a ton, but the more light it has, the greener it’ll be.

guppy grass care
guppy grass

If you’re looking for an amazing light, I suggest Fluval Planted 3.0 – but I wouldn’t drop that kind of cash on guppy grass, to be completely honest. If you like it for other reasons – there are a ton of reasons to love it – then by all means! But I’ve seriously used a cheap office clip lamp to grow this stuff no problem.

Planting or Floating Najas Grass?

You can either choose to plant it or leave it floating. One cool thing about guppy grass is that it displays something called heterophylly, which means that the leaf shape changes based on how it’s grown. So if it’s planted, the leaves will look different than if it was floated. This might sound like a neat little parlor trick on face value but, in reality, it means your plant has a fantastic chance of melting if you try to plant it after it’s been floating or visa versa.

Additionally, since this isn’t a substrate feeding plant, your chances of success greatly increase if you leave it floating. If you’re insistent on planting it, be aware that some report it breaks into dozens of pieces. Admittedly, I’ve never found the urge to attempt planting it myself so I can’t confirm. If you truly don’t want it left floating, opt for some plant weights and save yourself the headache.

If you find your najas is melting, I would be willing to bet its growing conditions have changed and it needs time to recover. It’s tempting to pump nutrients and light into the tank but resist the urge. It’s not going to speed it up and will probably just give you algae issues.

Substrate & Fertilizers

Guppy grass doesn’t need Co2, soils, or any fertilizers to grow. However, some fertilizers may help it grow if your water is incredibly soft and lacking nutrients. I have this problem with guppy grass in my water, so I do need to dose fertilizers, but unless you have crazy soft water or do a low water change schedule, this probably won’t be an issue for you.

If you opt to buy fertilizers, it uses liquid fertilizers. It obviously has little need for root tabs and substrate, and in most cases, won’t consume them (even if it’s planted!) If you’re looking for fertilizer suggestions, I’ve included some of my favorite tried and trusted fertz below. I will say that I haven’t found it to need additional nutrients outside of the all-in-ones below, but if your plant is still struggling after a few weeks you might want to consider adding liquid carbon.

Thrive C

This fertilizer is specifically for low-tech but heavily planted tanks. As with any fertilizer, a test kit and consistent monitoring for the first few weeks is essential. I wouldn’t be concerned with guppy grass not using all the available nitrates, but every tank is different. I would, personally, err on the side of caution and start slow with the dosage.


SeaChem Flourish

Flourish has been around for quite some time, they’re trusted, reliable and – overall – it presents very few issues. Particularly for the low-tech and low-maintenance plants. When you get into more expensive and needy plants, you’d likely need to tinker with dosing and purchasing additional supplements.


SeaChem Excel

Excel is the liquid form of Co2 (well, kinda.) So if you’re struggling with getting the best and fastest growth from your plants, experimenting with liquid carbon is a much cheaper alternative to a full-blown Co2 kit.

Common Problems

Najas grass doesn’t have a ton of problems, per se, but it can cause problems for you and your tank if left unchecked. Like most fast-growing plants, the plant grows faster than the tank space allows for in most cases. This can cause a problem if you don’t want your tank overrun with guppy grass, if you do, it might not be a problem for you.

Plant debris aquarium

Plant Debris

Plant debris in your tank is a relative problem. If you’re a breeder, your fry and shrimplets will likely enjoy picking off the infusoria and other critters that munch on decomposing plant matter. Similarly, if you have snails, this issue will likely never amount to much. And, so long as you’re not a neat freak, this issue probably won’t bother you.

However, if you don’t fall into one of those three buckets, the mess will probably infuriate you. Additionally, it may cause water quality issues as the plant decomposes and leaches everything it absorbed back into the water. 

shrimp cleaning java moss

Debris Collection

Mosses and other fine-leafed plants often attracts debris that settle and collect within it’s leafy clutches. This can give it a dirty or brownish appearance and, as we already discussed, most of these types of plants are difficult to clean up. This can be a problem if you don’t have a clean up crew likes snails, shrimp, or corydoras in your tank as this particulate matter can also – on top of being unsightly – block out light and slowly reduce growth in (or kill) the plant.

clogged aquarium filter

Clogging Your Filter

Funny thing; aquarium filters. They don’t need large particles to clog, just a lot of small particles. Of course, large floating masses of plants will also clog them. 

So as your plant multiplies, sheds, or decoposing plant matter turns into mulm and particulate matter, eventually all of it makes it way to – as you probably guessed – your filter! No matter your filter type; sponge, canister, hang on back, sump, you’ll likely have to up your regular maintenance schedule n your filter.

fast plant growth problem

Rapid Growth

While rapid plant growth is a great thing in most cases, it can also become a problem when it comes to regular upkeep on trimming, nutrients, and excess plant disposal. Since fast growing plants usually present an issue for local waterways and most are considered to be invasive species, taking care to properly dispose of excess is incredibly important.

In addition, it’s quite possible that it can choke out your other plants by out-competing them for nutrients. This can, of course, be remedied by changing the water more frequently, adding more fertilizer to the water, or keeping up on trimming of the faster growing plants. But, since trimming and disposal also comes with it’s own issues, this last option is probably the most time-consuming.

aquarium plant deficiencies

A Lack Of Nutrients

Fast growing plants can cause two – er, maybe three – major nutrient issues.

  1. They can choke out other plants by out-competing them for nutrients. Eventually the plants that can’t compete will slowly die. 
  2. They can soak up so many nutrients that they choke themselves out.
  3. They can out-compete your fish for the same nutrients in the water – especially fry. 

You can fix this issue by doing more water changes to replace nutrients or you can add fertilizers to the water to similarly replace nutrients. Although, both methods will require some tinkering and fine-tuning to get right.


Maintaining guppy grass is basically nonexistent. Unless your tank becomes overrun with it, you experience algae issues – which is highly unlikely -, or it starts choking out your other plants, you’re unlikely to have to maintain it at all.

In order to keep it in balance, I suggest trimming it every few weeks or so when it starts to get overrun. Thick masses can prevent light from reaching the bottom of the tank, which can be an issue if you have other plants in your tank. If you don’t, this might not be an issue for you and you’ll likely never have to touch it. Keeping up with disposal and trimming is probably the biggest issue you’ll face with najas grass.

Preventing najas grass from getting into local waterways – even if it’s native to where you live – is important for the balance of the local ecosystems. This is particularly true for those who live near wetlands. Since guppy grass grows in such abundance, getting rid of it may be a weekly chore for some. You can bury it (even in your garden for nutrients like you can with duckweed,) add it to your compost heap, or use a bleach soak to kill it before throwing it away (or soak it long enough to dissolve it in bleach.) If that all sounds like too much, you can throw it away in plastic bags to prevent it from getting into local water bodies – although, then you may be introducing more plastic waste into waterways and oceans.


Guppy grass will grow both longer, as well as send off side shooters. You can snip pieces of the plant off and these clippings will continue to grow as well. The hard part isn’t propagating at, it’s trying to keep it under control. If you become overrun you can certainly sell it online or at your local fish store, they will gladly take it from you as it’s always in demand.

Unless you have multiple tanks or a way to sell and distribute cut pieces, it’s probably safest not to propagate guppy grass (lest you be overrun with it!)

Benefits Of Guppy Grass

Guppy grass is especially useful if you plan on breeding livebearing fish, eggs scatterers, or shrimp. Other than in a breeding set up, it may be helpful in a pond setup. Although it doesn’t overwinter as well as hornwort.

It’s also incredibly useful in fry grow out tanks as it grows fast enough to keep up with the bioload. Guppy grass is also an exceptional plant for beginners. It can help absorb any water change mistakes you may make – like overlooking tap water conditioner, forgetting a water change, or overstocking.

It’s also a hardy plant that will certainly help prevent any algae issues. The only problem with guppy grass is that it will eventually overrun your tank if left unchecked. If this isn’t an issue for you, then you’ll get along just fine.

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