PhosGuard 500 ml — Anti-Phosphate Spherical Aluminum Oxide | Seachem

Seachem PhosGuard 500ml is a bulk-form, spherical aluminum oxide filter media that quickly removes phosphates and silicates from marine and freshwater aquariums. Its unique spherical bead shape—unique in the phosphate control market—prevents compaction and promotes optimal water flow for maximum effectiveness. The 500ml size offers excellent value for money for medium to large reef aquariums requiring regular phosphate control.

Main advantages

• Rapidly removes phosphates and silicates — capacity of 0.87 mg PO4/g
• Unique spherical shape on the market — optimal water flow, no compaction
• Irreversible bond — does not release phosphates or silicates into the water
• Economical 500 ml bulk format — divisible into several treatment portions
• Inert and safe — can remain in the filter indefinitely without risk

Use in reef and marine aquariums

High phosphate levels promote the growth of unwanted algae and impair coral growth and coloration. PhosGuard absorbs phosphates very quickly—reaching full capacity in 4 to 5 days in the presence of high phosphates. Seachem recommends continuous use of small amounts rather than intermittent use of large amounts. PhosGuard works best in saltwater and at alkaline or neutral pH. Under reef conditions (pH close to 8), no detectable soluble aluminum is released, according to Seachem's controlled studies, and soft corals remain unaffected even at three times the recommended dosage.

Instructions for use

• Pre-wet by adding the product to twice its volume of fresh water, then rinse. Do not add water to the dry product. Do not use seawater for the initial wetting (risk of excessive heat).
• Place in a filter bag (recommended) in a cartridge filter, media chamber, box filter, or any high-flow area — do not use in a media reactor
• Dosage: 85 ml (⅓ cup) per 200 L (50 US gallons) of seawater or 400 L (100 US gallons) of freshwater
• Leave in place for 4 days, then test the phosphates. If the concentration has not decreased to 0.02 mg/L, replace the PhosGuard.
• If the levels remain under control, the product is not depleted — leave it in place and test weekly.
• PhosGuard can be removed, dried, and put back into service as long as it is not exhausted.

Manufacturer's precautions

• May generate heat upon first contact with water — always pre-wet with fresh water when adding the product to the water, never the other way around
• The yellowing of the medium indicates the absorption of organic compounds, not the depletion of phosphates.
• Do not overdose — too rapid a drop in phosphates can stress sensitive corals
• Aluminum oxide is NOT regenerable — cooking does not restore its absorption capacity
• Not recommended for phosphate-buffered freshwater aquariums

Comparison of Seachem anti-phosphates

• PhosGuard (aluminum oxide): 0.87 mg PO4/g — rapid absorption, spherical shape
• PhosBond (GFO + aluminum oxide hybrid): 1.19 mg PO4/g — intermediate capacity
• PhosNet (GFO): 1.41 mg PO4/g — highest capacity

Available formats

• 100 ml (sachet)
• 250 ml
• 500 ml
• 1 L
• 2 L
• 4 L

Why choose PhosGuard from ReefSolution?

The 500 ml size is the economical choice for aquarists who regularly dose in small quantities. Place it in the Seachem The Bag for optimal use. For higher binding capacity per gram, consider Seachem PhosBond or Seachem PhosNet. Monitor your phosphate levels with the Hanna Checker Phosphate or the Salifert Phosphate Test Kit.

Frequently Asked Questions

Can PhosGuard be used in a media reactor?

No. Seachem does not recommend this because agitation in a reactor reduces the media to dust. Use in a cartridge filter, media chamber, or any high-flow area with a filter bag.

What is the difference between PhosGuard, PhosBond and PhosNet?

PhosGuard (aluminum oxide, 0.87 mg PO4/g) absorbs rapidly and has a unique spherical shape. PhosBond (GFO + aluminum oxide hybrid, 1.19 mg PO4/g) offers intermediate capacity. PhosNet (pure GFO, 1.41 mg PO4/g) has the highest binding capacity per gram.

Can PhosGuard be dried and reused?

Yes. The PhosGuard can be removed, dried, and reused as long as it is not depleted. It does not release phosphates or silicates. However, it is not regenerable—once its capacity is reached, it must be replaced.