PhosGuard — Spherical Aluminum Oxide Anti-Phosphate and Silicate 100 ml to 4 L - Seachem

Seachem PhosGuard 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 — prevents clumping and maximizes water contact for superior effectiveness.

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
• Available from the 100 ml sachet up to the 4 L bulk size
• 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 hinder coral growth and coloration. 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 effectiveness, not low capacity. Seachem recommends using small amounts continuously rather than large amounts intermittently. PhosGuard works best in saltwater and alkaline pH. Under reef conditions (pH close to 8), no detectable soluble aluminum is released.

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 per gram

Available sizes

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

Why choose PhosGuard at ReefSolution

The 1 L format is ideal for aquarists who want a supply of phosphate-removing media ready for multiple treatment cycles. To round out your routine:

• Seachem The Bag — the recommended filter bag to hold the media in your filter
• Seachem PhosBond — GFO + aluminum oxide hybrid, intermediate capacity (1.19 mg PO4/g)
• Seachem PhosNet — pure GFO, the highest capacity per gram (1.41 mg PO4/g)
• Salifert Phosphate Test Kit — to measure your level before and during treatment

Frequently Asked Questions

How many treatments does the 1 L format provide?

At the standard dosage of 85 ml per 200 L of seawater, the 1 L format provides approximately 11 treatment doses. For a 200 L aquarium with controlled phosphate levels, this represents several months of continuous use.

What is the difference between PhosGuard, PhosBond and PhosNet?

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

Can PhosGuard be used in a media reactor?

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