Glush Weed

About

Hygrophila costata is the odd one out among aquarium hygrophilas: the only American species in general trade, native to Florida, the Caribbean, southern Mexico and Central and South America, while every shop-shelf relative is Asian. Flowgrow adds the warning the label leaves off - the aquarium plant trade carried it to Queensland, where it is now considered invasive - so trimmings go in the bin or the compost, never in a ditch. A settled stand is strictly upright: smooth, roughly square stems about 4 mm thick carrying pairs of very narrow, almost ribbon-like light-green leaves every 4-5 cm. How long those leaves get is genuinely disputed - Aquasabi measures 20-24 cm by 8-10 mm, Tropica says about 10 cm - so buy it for the narrow shape, not for a promised length. No source we checked records a red or bronze form and every one of them calls the leaf light green; treat that as an untested colour rather than a proven one, but do not buy this plant expecting light or iron to colour it. The shop label is the real minefield. Tropica states of its own 052A that the plant 'was called Hygrophila corymbosa Angustifolia until recently', while Flowgrow keeps H. corymbosa 'Angustifolia' as a separate Asian entry with distinctly different water: KH 2-18 and pH 5.5-7.5 against costata's KH 0-7 and pH 5-7, difficulty 'very easy' against costata's 'medium'. Submersed the two are near-identical and there is no counter-top test: the definitive tell is the flower on emersed shoots, white in H. costata against the light purple to pink of the Asian H. salicifolia group, which a submersed pot will never show you. The water bands are a consequence of which plant you have, not a way to find out. The American trade names 'willow hygro' and 'hygro willow' belong to that Asian plant - Aquarium Co-Op sells them as Hygrophila angustifolia - not to this one. Against the rest of our catalogue it separates easily: dwarf hygrophila has 3-5 cm leaves, water wisteria's leaves are pinnately cut, Hygrophila pinnatifida is serrated with brownish tones and climbs hardscape, and temple plant's leaves are far wider. When unhappy it stalls or goes leggy at the base rather than melting away.

Care

The band most likely to catch you out is hardness, not light. Flowgrow and Aquasabi both cap this species at 7 dKH with pH 5-7, so it is a soft, acid-water plant in a market whose tap water mostly is not - much of Lithuania runs well above 7 dKH, and untreated hard tap water is already outside its range. That is a large part of why one keeper's 'hygro' romps away and another's sulks: the easy one is usually the Asian lookalike, which Flowgrow rates to 18 dKH. Cut with RO, or buy temple plant instead. CO2 is contested and we resolve it the demanding way: Aquasabi lists CO2 as needed and Flowgrow targets 20-40 mg/l, while Tropica alone rates the demand low - without injection expect slow, sparse shoots rather than a dead plant. It is a heavy feeder; Flowgrow asks for NO3 10-50, PO4 0.1-3, K 5-30 and Fe 0.01-0.5 mg/l, and starved leaves yellow then brown. On light, Flowgrow says medium to high and Aquasabi's only lighting note is that it should not be lit too dimly; on the near-identical Asian willow hygro, Aquarium Co-Op spells out what too dim looks like - the bottom of the stem drops its leaves and leaves a bare, leggy base. Shop pots are emersed-grown, so Tropica's rounder, wider-spaced leaves melt back after planting while narrow submersed ones regrow: adaptation, not disease. Top the stems regularly and replant the cuttings before the tops shade the lower stand.

Frequently asked questions

What water parameters does a Glush Weed need?

Glush Weed does best at 18–30 °C (64.4–86 °F), pH 5–7 and a general hardness of 0–30 °dGH.

Where should Glush Weed be placed in the aquarium?

Glush Weed works best at the back of the tank and reaches around 60 cm.

Is the Glush Weed suitable for beginners?

Glush Weed sits in the middle of the difficulty scale — manageable for a careful beginner who has done the reading, but it has specific needs worth researching first.

Sources

• Flowgrow Aquatic Plant Database - Hygrophila costata (Glush weed)
• Tropica - Hygrophila costata (052A)
• Aquasabi - Hygrophila costata
• Flowgrow - Hygrophila corymbosa 'Angustifolia' (the Asian lookalike)
• Aquarium Co-Op - Willow Hygro (page sells Hygrophila angustifolia, the Asian lookalike)
• Wikipedia - Hygrophila costata