Guppy grass: the breeder's best friend
Najas guadalupensis
A fast, bright tangle that floats or plants anywhere and shelters fry.
Where it comes from
Najas guadalupensis is native to the Americas, growing in ponds, ditches and slow streams from North to South America. It is an adaptable, fast-growing plant that lives happily rooted in the substrate or drifting as a loose floating mass.
What to expect
Guppy grass forms a bright green tangle of thin, brittle, branching stems lined with narrow leaves. It has no strong up-or-down orientation — it simply grows into a soft, dense thicket, which is exactly what makes it such good cover.
The case for guppy grass
Left floating, guppy grass forms a dense thicket at the surface that newborn livebearer fry and baby shrimp disappear into, safe from hungry adults. At the same time it grows so fast that it strips ammonia and nitrate from the water as quickly as almost any plant, keeping a crowded fry tank clean. No substrate, no fertiliser, no CO2 — just drop it in.
How to keep it
There is essentially nothing to do. It grows in cold water and warm, hard water and soft, bright light and dim. Its only vice is that brittle stems shed fragments when handled, and every fragment can grow into a new plant — so it spreads readily.
| Parameter | Value |
|---|---|
| Lighting | Low to high — grows under almost any light |
| CO2 | Not required |
| Temperature | 15–30 °C |
| pH | 6.0–8.0 |
| Hardness | Soft to hard |
| Fertiliser | Not needed; feeds on tank waste |
| Substrate | Any, or none — floats |
| Growth rate | Very fast |
| Placement | Background or floating |
| Difficulty | Easy |
What goes wrong
The main complaint is mess: brittle stems break easily and bits get drawn into filter intakes. Thin it regularly and net out loose fragments. If a large floating mat suddenly melts and fouls the water, it is usually a sharp change in temperature or chemistry — introduce it gradually and keep a modest amount rather than a thick raft.
More plants in this series
- Hornwort (Ceratophyllum demersum) — the other rootless fast grower
- Water sprite (Ceratopteris thalictroides) — lacy fern, plant it or float it
- Anacharis (Egeria densa) — the classic fast oxygenator
- Duckweed (Lemna minor) — the tiny floating nutrient sponge