• General Overview

  • The Knob Sea Star (Protoreaster nodosus), also known as the Horned Sea Star, is a stunning marine invertebrate prized for its vibrant colors and distinctive knobby texture.

  • Available at 8–15 cm, these medium-sized specimens are ideal for established reef or marine aquariums.

  • Its striking appearance and slow, graceful movement make it a standout addition for hobbyists who enjoy diverse invertebrates.

  • A hardy species, it is suitable for beginners with proper care and stable water conditions.

• Appearance & Coloration

  • Thick, rigid body covered with prominent knobby projections (the “knobs” or “horns”).

  • Colors vary from bright red, orange, or brown with contrasting beige or cream knobs.

  • Five arms radiate from a central disc, giving it a classic star shape.

  • Surface texture and pattern make it a visually interesting focal point in aquariums.

  • Color becomes more vibrant with good nutrition and clean, stable water.

• Temperament & Behavior

  • Peaceful and slow-moving, ideal for reef tanks.

  • Moves gradually along the substrate using tube feet.

  • Often grazes on detritus, leftover food, and small invertebrates.

  • Non-aggressive toward other tank inhabitants.

  • Prefers resting on sand, rubble, or rock surfaces.

• Adult Size & Lifespan

  • Adult size: 15–30 cm in full growth, but aquarium specimens often start at 8–15 cm.

  • Lifespan can reach 10–15 years with proper care.

  • Growth is slow and steady, requiring time and stable nutrition.

• Tank Size & Aquarium Setup

  • Minimum tank size: 100 liters (25 gallons), larger recommended for multiple invertebrates.

  • Needs fine sand or rubble substrate to prevent injury and facilitate natural movement.

  • Avoid sharp rocks or corals that could damage tube feet.

  • Moderate to low water flow is preferred; strong currents may stress the sea star.

  • Include live rock or reef-safe décor for shelter and grazing surfaces.

• Water Conditions (Marine Parameters)

  • Temperature: 24–27 °C

  • Salinity: 1.023–1.025 SG

  • pH: 8.1–8.4

  • Alkalinity: 8–12 dKH

  • Ammonia & Nitrite: 0 ppm

  • Nitrate: Below 10–20 ppm

  • Stable marine conditions are critical for health; sudden parameter shifts can be fatal.

  • Weekly water changes of 10–20% are recommended.

• Feeding Habit & Diet

  • Omnivorous scavenger with a preference for detritus and small invertebrates.

  • Can feed on:

    • Leftover meaty foods (shrimp, fish, mollusks)

    • Algae

    • Specialized sea star pellets

    • Micro-invertebrates in live rock

  • Feed 1–2 times weekly, ensuring food reaches the substrate where the sea star can access it.

  • Overfeeding can cause water quality issues; monitor nutrient levels closely.

• Tank Mates & Compatibility

  • Reef-safe when kept with non-aggressive fish and invertebrates.

  • Compatible with corals, clams, snails, and peaceful fish.

  • Avoid predatory or highly mobile fish that may nip or disturb the sea star.

  • Not suitable with certain small or soft-bodied invertebrates, as they may become prey.

• Care Level & Maintenance

  • Care level: Intermediate

  • Requires established aquariums with mature, stable water parameters.

  • Sensitive to sudden changes in salinity, temperature, or pH.

  • Minimal daily care—mainly monitoring water quality and occasional supplemental feeding.

• Health & Special Notes

  • Hardy species but sensitive to poor water quality or incompatible tank mates.

  • Tube feet are vulnerable—ensure smooth substrates to avoid damage.

  • Avoid copper-based medications, which are toxic to sea stars.

  • If stressed, may retract arms or become immobile; stable conditions usually resolve this.

• Why Choose Knob Sea Star (8–15 cm)?

  • Striking knobby texture and vibrant coloration

  • Peaceful, slow-moving, and reef-safe

  • Adds natural movement and interest to marine aquariums

  • Hardy with proper care and established water conditions

  • Long-lived in stable, well-maintained tanks

The Knob Sea Star (8–15 cm) is a visually stunning and low-maintenance invertebrate that enhances the beauty of any marine aquarium. With stable water parameters, a suitable substrate, and occasional feeding, this species will thrive and become a long-term centerpiece in your reef or saltwater tank.