The Salty Side: Saltwater Aquariums for Beginners

How to Dose Phosphates in a Saltwater Aquarium

Chances are you have stumbled across this article because you need to know how to increase phosphates without the added disadvantage of over-feeding.  You may have tried just about everything but nothing seems to work and they remain undetectable. We all know that keeping coral requires that you have to have trace amounts of phosphate in your system.  However, if your system is too efficient at exporting nutrients, because of your coral consumption rate, or simply because your system is too ‘clean’, this is when you will need to know how to dose phosphates in a saltwater aquarium.

How to dose phosphates in a saltwater tank

Why dose phosphates in a saltwater tank?

Apart from the trace amounts of phosphate required for coral consumption, phosphate is integral to the marine environment in your aquarium. Without phosphate, not only will your coral eventually die, but you will also be opening the door to unwanted problems such as dinoflagellates. If you are simply unable to maintain adequate phosphate levels through feeding your fish and corals alone, then dosing comes with a few benefits too.

1. Overfeeding to increase phosphate

Overfeeding your tank will result in very happy fish, but this also has the potential to increase the amount of dissolved organics in your system. Not only does this turn your water a yellow hue, but can be attributed to unwanted algae growing in your tank too.

Dosing phosphate will increase phosphate only.

2. Inability to decrease nitrate

Nitrate and phosphate go hand in hand. With no phosphate, or even limited phosphate, in your aquarium, nitrate levels will remain static. No matter how you try to bring your nitrate down, it may not move at all. Not until you increase your phosphate.

By dosing phosphate, you will be aiding the potential ability to export nitrate more efficiently.

3. Maintaining stable phosphate levels

Once you have been dosing phosphate in a saltwater aquarium for a while, you will soon to able to ascertain how to maintain your phosphate level exactly where you want it to be, not where it may be due to feeding. This should be relatable to the Redfield Ratio.

4. Dosing phosphate is cheap

Tri-sodium phosphate is purchased in powder form and diluted in RO water. The dilution rate requires the smallest amount of powder ensuring it lasts for a very long time.

Of course, if you would rather use a ready mixed product, Brightwell Aquatics NeoPhos will fit the bill.

Brightwell Aquatics NeoPhos - Phosphorus Supplement for Ultra-Low Nutrient Reef Aquarium Systems, 500ml
  • Recommended for advanced reef aquarists for maintaining low nutrient reef aquariums
  • May be used with MicroBacter7 Reef BioFuel NeoNitro or Katalyst to improve health and coloration of inhabitants
  • Lowers ammonia nitrite and nitrate concentrations without the use of chemical filtration media and pollution

5. Total control of phosphate in a saltwater aquarium.

Dosing phosphates in a salt water tank gives you complete control. Once you become used to dosing, any desired level can be achieved and maintained. Once mixed, you could also consider using an auto-doser to automate your dosage requirement.

6. Dosing phosphate to get rid of dinoflagellates

The influx of dinoflagellates in a system is known to be attributed to the bottoming out of nutrients, among other reasons. The quickest and cleanest way of raising your phosphate is through dosing, if you have a nutrient deficient aquarium.

Dosing phosphate in a saltwater tank with TSP

There are a few choices available when thinking about dosing phosphate. We will only focus on two here, both of which have proven to work for me. The first and cheapest to use is food grade Tri-Sodium Phosphate. This is used as a cleaning solution, but in the hands of a reefer in the correct concentration it is harmless in a saltwater tank, and your corals will thank you.

This is a guide to start you off, as each tank is different. In fact I have had different results in both my frag tank and my display tank.
You will soon discover what your tank needs in order to bring phosphate to the level you desire.

Tri-sodium phosphate dosage and mixing rate

Tri-Sodium Phosphate is easily diluted in RODI water in the following mixing ratio:

Using a gram scale, measure out 1.88g of powder. Add this to 1 litre of RODI water. To raise your phosphate by 0.01ppm, add 1ml per 100L of aquarium water.

I would use the above dilution as a starting point.  You may need to double the Tri-Sodium Phosphate amount to 3.76g/L in order to see a noticeable increase per dose, which is what I did.

MAXUS Precision Pocket Scale 500g x 0.01g, Digital Gram Scale with Tray, Small Food Scale, Jewelry Scale, Ounces Grains Scale with Backlit LCD
  • [Gram Scale] Features Smart-Off (TM), Foolproof Calibration (TM) Technology and Overload Protection, Batteries Included
  • [Pocket Scale] Capacity x Readability: 500g x 0.01g / 17.636oz x 0.001oz / 7716.1gn x 0.2gn / 2500ct x 0.05ct / 16.07ozt x 0.001ozt / 321.50dwt x 0.01dwt
  • [Grain Scale] Units of Measure include: Grams, Ounces, Troy Ounces, Pennyweights, Carats, Grains; Arrow Scale, Archery Scale

If your system is completely phosphate deficient, you may not even see an increase in the beginning, as your corals hungrily consume all the phosphate they have been lacking, as soon as you add it to your tank. Eventually however, you will get to the point when phosphate becomes detectable. At this point you can start taking note of how much your tank requires over any given period.

Depending on the deficiency of your system, you may need to repeatedly dose until you eventually have a reading.

The alternative to Tri-sodium phosphate would be Brightwell Aquatics NeoPhos. Although this is the more expensive option, it is ready mixed and ready to dose phosphates in a saltwater aquarium.

So there you have it!

My requirement to dose phosphate was borne of the need to get rid of dinoflagellates. When setting up my new tank both nitrate and phosphate hit zero. Nitrates climbed eventually but nothing helped to raise phosphate, and dino continued to plague my tank.

I turned to dosing Tri-Sodium Phosphate.

Over a period of two days my PO4 went from 0ppm to 0.12ppm (which I specifically aimed for).  I did double the solution mix in order to increase the dosed amount, making the 1L solution go further.

I tend to find that in my tanks, the doubled solution raises PO4 by 0.01ppm/13ml dosed.


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