Aquarium Phosphate Levels

Maintaining The Right Phosphate Levels

Phosphates are highly reactive compounds that are essential to living creatures. All living things use phosphates both as a source of energy and for bio-chemical reactions, vital to their continued functioning.

In your aquarium, phosphates will be one of two forms:

  • Inorganic (orthophosphate)
    Phosphate in this form is water soluble and plants can easily absorb it.
  • Organic
    This is phosphate that’s bound chemically in cells. In order for it to be reactive, bacteria must first break down the cell to release the phosphate.

The main concern of having excess phosphate in your saltwater aquarium is that algae uses it for food. At the mild end, having excess algae is annoying because they grow on rocks, aquarium tank walls, and other surfaces. If this continues, your water will eventually turn green and become murky.

On the other end of the spectrum, in a severe outbreak, the algae will consume and deplete oxygen from your aquarium, eventually killing all living creatures.

However, algae growth need a supply of phosphates, nitrates, and light (artificial or natural). By keeping any one of these three low, you can control algae.

But by keeping all 3 in the correct balance, it gives you some latitude, in case another factor becomes unbalances for some reason.

If you’re maintaining a reef or semi-reef tank and you’re concerned about coral growth, phosphate levels higher than 0.25 ppm, it can inhibit their growth.

Maintaining the right phosphate balance is vital to your saltwater aquarium ecosystem.

Phosphate Sources

There are two main phosphate sources in your saltwater aquarium:

  • Internal sources
    There are several sources that originate inside your aquarium

    • Dead plant material
    • Feces
    • Uneaten food particles
    • Bacteria
  • External sources
    These are sources you can control through careful monitoring

    • Water supply
    • Additives in foods (i.e. flakes, frozen shrimp)

Controlling Phosphate Levels

The best way to control phosphate levels is to control their influx. The primary source of phosphate in a saltwater aquarium is through the food source. 5 grams of fish flake food can raise the phosphate levels by 0.5 ppm.

Ideally, the phosphate levels should max out at 0.5 ppm and should hover around 0.1 ppm.

If you keep reef or semi-reef tanks, the live plants and organisms living on the rock will absorb and use the phosphate, helping control their levels.

Ironically, you can use one of the major concerns with high phosphate levels to control it: algae. By keeping macro algae (i.e. filtration system, sump, refrigerium), because they consume phosphate, they can keep phosphate levels low.

Along the same lines, live mangrove plants are highly effective in binding water soluble phosphates. These plants are so effective at not only removing phosphates but nitrates and other organic material, they stopped using protein skimmers.

Protein skimmers can help control phosphate levels by removing excess organic material (i.e. feces, uneaten food particle) that will break down into nitrates and phosphates.

Phosphate Test Kits

Phosphate test kits are useful in monitoring phosphate levels. However, they can only measure inorganic phosphate that’s dissolved in your saltwater.