Guppy grass, najas grass, or – scientifically – Najas guadalupensis, is a fast-growing plant that removes heavy metals, toxins, ammonia, nitrite, 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!
Disclosure: we’re reader-supported! So if you buy a product I recommend, I might make some coffee money at no cost to you.
Table of contents
Guppy Grass FAQ
Does guppy grass need light?
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.
How fast does guppy grass grow?
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.
Are there any fish that eat guppy grass?
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 Care
Difficulty: Easy – although disposal may become an issue
Size: 3’+ (almost a meter)
Propagation: Side shoots, clippings, and vertical growth
Speed of growth: Quickly
Temperature: 50 – 86F (10 – 30C)
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.
Fluval Plant 3.0 Light
Rating: 4.8 stars
Price: $150 – $210 *size dependent
Par: 45 at 24″
I love this light. It’s expensive, so prepare for a sticker shock, but it’s totally worth every penny of the price tag. It’s a fully customizable, automatic, and adjustable light that I can’t get enough of. Plus, it doesn’t have a remote, it’s controlled by your phone, so it fixes all the issues that the Finnex 24/7 had.
You know, like the remote not working six months after you bought it kind of thing.
Finnex Planted+ 24/7
Rating: 4.7 stars
Price: $67 – $106 *size dependent
Par: 58 at 24″
My one issue – everyone’s issue, really – is that the remote gives out. If you don’t care about being able to control it, it’s a great light. If you’re excited about it being “fully” customizable (it’s not compared to the Fluval 3.0,) then this probably isn’t the light for you.
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.
Rating: 4.4 stars
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.
Rating: 4.8 stars
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. More expensive and needy plants will likely need tinkering with dosing and additional supplements.
Rating: 4.7 stars
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.
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.
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.
I’m so glad I found your site because finding a care article on guppy grass is so tough! I feel really stupid, but I keep killing mine. I don’t understand. It goes soft and mushy and brown and dies on me every time. What’s wrong with it? I can’t figure it out and I’m ready to swear off plants for good.
Don’t feel stupid, I’ve literally killed duckweed before, so you’re in good company! One big issue most people have with guppy grass is they try to plant it when it was grown floating or visa versa. Because the leaf structure is dependent on how it’s grown, the leaves will melt if you do the opposite.
If you are growing it floating, that’s prob not the issue here and it’s likely a nutrient thing. You can email me some pictures of it with your tank readings (pH, ammonia, nitrite, and nitrate) and I can try to help more. Or you can post the reading here if you feel like it, I’m sure someone else would find it useful. It’s a lot more common than you probably think.
Thanks so much, I’ll email you if that’s okay?
Totally! I’ll see what I can do to help.