PhosGuard 100 ml Sachet — Spherical Anti-Phosphate Aluminum Oxide | Seachem

Seachem PhosGuard 100ml pre-packaged filter media is a spherical aluminum oxide-based filter media that quickly removes phosphates and silicates from marine and freshwater aquariums. Its unique spherical bead shape—unique in the phosphate remover market—promotes optimal water flow through the media, increasing its efficiency and capacity compared to competing granular media that compact and limit contact with water.

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
• Ready-to-use 100ml sachet format — ideal for aquariums up to 235 L (60 US gallons)
• Inert and safe — can remain in the filter without risk

Use in reef and marine aquariums

High phosphate levels promote the growth of unwanted algae and are detrimental to coral health. PhosGuard absorbs phosphates very quickly—reaching full capacity in 4 to 5 days in the presence of high phosphates. This rapid replacement rate is a sign of efficiency, not low capacity. Seachem recommends using small amounts continuously rather than large amounts intermittently. PhosGuard works best in saltwater and at alkaline or neutral pH. Under reef conditions (pH close to 8), no detectable soluble aluminum is released.

Instructions for use

• The 100ml sachet is pre-packaged and ready to use.
• Place in a cartridge filter, media chamber, box filter or any high-flow area — do not use in a media reactor (agitation produces dust)
• 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 in place
• Test phosphate levels weekly until they rise to determine when to replace

Manufacturer's precautions

• May generate heat upon first contact with water — pre-wet by adding the product to twice its volume of fresh water. Do not add water to the dry product. Do not use seawater for the initial wetting (risk of boiling).
• 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
• Aluminium oxide is NOT regenerable — cooking does not restore its ability to absorb phosphates.

Comparison of Seachem anti-phosphates

• PhosGuard (aluminum oxide): 0.87 mg PO4/g
• PhosBond (hybrid GFO + aluminum oxide): 1.19 mg PO4/g
• PhosNet (GFO): 1.41 mg PO4/g

Available formats

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

Why choose PhosGuard from ReefSolution?

The 100ml sachet is ideal for nano aquariums or as a first phosphate treatment. For superior binding capacity, consider Seachem PhosBond (GFO + aluminum oxide hybrid) or Seachem PhosNet (pure GFO). Monitor your phosphate levels with the Hanna Checker Phosphate or the Salifert Phosphate Test Kit. Place PhosGuard inside the Seachem The Bag for bulk quantities.

Frequently Asked Questions

Can PhosGuard be used in a media reactor?

No. Seachem does not recommend it because agitation in a reactor can reduce the media to dust. Use in a cartridge filter, media chamber, or any area with high static flow.

Does PhosGuard release aluminum that is toxic to corals?

No. Seachem's controlled studies demonstrate that under reef conditions (pH close to 8), no detectable soluble aluminum is released. Even at three times the prescribed dosage, soft corals remain unaffected.

Why does PhosGuard need to be replaced every 4 days?

Frequent replacement is a sign of effectiveness, not low capacity. PhosGuard absorbs phosphates so quickly that it reaches full capacity in 4 to 5 days in the presence of high phosphates. Once levels are under control (below 0.02 mg/L), leave it in place and test weekly.