Guppy Grass | Najas guadalupensis
Guppy Grass
Scientific Name: Najas guadalupensis
Common Names: Southern Waternymph, Guppy Grass, Najas Grass, Common Water Nymph
Guppy grass (Najas guadalupensis) is a fast-growing freshwater plant native to the Americas from Canada down to South America, with introduced populations in Japan, Palestine, and Israel. Najas grass can be rooted in the substrate of your blackwater, biotope, or botanical method aquarium, or left floating at the surface. It gets its name from its ability to provide excellent shelter for baby fish, offering them protection from larger fish, while providing an abundance of surface area that grows supplemental nutrition for their early stages of life.
Guppy grass is quite hardy, and its ability to absorb excess nutrients makes it ideal for the beginner aquarist. Since it floats so close to the aquarium lights, it can help provide shade and cover to the ecosystem below. But, make sure that if its growth gets too dense, to pick low-light aquatic plants for the substrate below.
Caring for Guppy Grass in Blackwater Aquariums
Sold as: You will receive 1/4lb of Guppy Grass.
Care Level: Easy
Lighting Requirements: Low to Medium
CO2: Not needed
Tint Tolerance: Low to High; if left floating, this plant tolerates higher levels of tint
Growth Rate: Fast
Native Habitat: North America, Central America, and South America
All Plants may contain snails or snail eggs. We keep them in all of our tanks for the benefits they provide. Our blackwater aquarium plants are provided by H2OPlants in adherence to their Shipping and DOA Policies. Your curated selection will arrive in their packaging separate from your botanical & merch orders.
Home is getting a bit more natural
While the aesthetic appeal of botanicals and tinted water can be quite attractive to us, the recreation of nature to emulate water conditions, feeding patterns, spawning displays, and territory building are the true benefits botanicals provide to our critters.
Botanical FAQs
Compostable Packaging Promise
Our packaging is designed to return safely to the Earth, just like the botanicals inside. Every bag is BPA- and Phthalate-free, GMO-free, and contains no animal products. Each meets ASTM D6400 composting standards, ensuring it can fully break down in a home compost bin.
What are the Fluffy White Growths on my Botanicals?
That’s biofilm and fungi—what we call the “goo phase.” It’s one of the clearest signs that your aquarium is alive and functioning. These growths wax and wane naturally as botanicals decompose. They’re harmless, even beneficial, and will disappear on their own once microbial populations stabilize.
Will botanicals lower the pH of my water?
That depends entirely on your source water. In very soft or RODI water, botanicals can gradually lower pH as tannins and humic substances accumulate. In medium to hard tap water, buffering capacity often resists these shifts, and you may not notice much change. At Betta Botanicals HQ, our very hard water (350+ ppm) shows almost no pH change unless we use botanicals like Alder Cones or Macaranga Leaves.
When should I replace leaves or pods in my tank?
We recommend allowing botanicals to fully break down into detritus, since this fuels microbial life and enriches the substrate. You can remove them once they stop tinting the water, but you’ll lose some of their ecological benefits. Each time you add new botanicals, follow proper preparation and observe your livestock until you learn your aquarium’s rhythm.
Are your products just for bettas?
Nope. Our botanicals are safe for almost all aquariums, terrariums, vivariums, and paludariums. The only exceptions are goldfish and axolotls, which may ingest small pods like alder cones or casuarina cones. For those species, we recommend large leaves such as Indian Almond, Loquat, or Jackfruit.
What are Tannins?
Tannins are natural compounds released by leaves, seed pods, and bark as they decompose in water. They soften water, gently lower pH, and create the characteristic tea-stained tint found in blackwater habitats. But their role goes far beyond color—tannins fuel beneficial bacteria, fungi, and biofilms, which form the foundation of a healthy ecosystem. They also offer mild antifungal benefits and help reduce stress in fish by replicating the natural conditions they’ve evolved in. At their core, tannins are plant-derived antioxidants that connect your aquarium to the same processes at work in wild flooded forests and streams.