Mon-Thurs 7am-5pm PST
Fri 7am-4pm PST

Questions about products, orders, shipping?
Contact us by call or email

How to Remove Phosphates from a Saltwater Aquarium By Joseph Chang, MarineDepot.com Reef Squad

  • Marine Depot
  • Aug 8, 2012

A common problem in marine fish and reef aquarium systems is high levels of phosphate. Phosphate can come from food added to the aquarium, fish waste, fish and coral respiration, low-quality carbon, impure water added to the tank along with numerous other causes.

Hanna Instruments Checker Phosphate Colorimeter

Phosphate is present in every aquarium and exists in two forms: organic phosphate and inorganic phosphate (mainly orthophosphates). Organic phosphate breaks down over time into orthophosphates through natural biochemical processes. The accumulated orthophosphates in turn are taken up readily by nuisance algae and will inhibit calcification, which retards coralline algae and coral growth. Elevated phosphate levels also boost the growth of brown algae pigments in SPS which can cause the corals to turn brown. Ideally, you want to keep your phosphate level below 0.03 ppm in a reef aquarium to minimize nuisance algae growth and promote the health and color of your corals.

A good test kit is pivotal in your fight against phosphates. Salifert and Elos both offer excellent test kits you can use to test for orthophosphates. The Hanna Checker Phosphate Colorimeter is also quite popular. Hanna’s Phosphate Meter is another option that, while more expensive, provides extremely accurate results in an easy-to-read digital readout.

Your first line of defense is to reduce the amount of phosphates going into your tank. If you are feeding frozen food or are soaking your food in liquid supplements, be sure to discard any liquid the food is being soaked in. Do not over feed your fish either because uneaten food can rapidly raise phosphate levels. You should also be sure the water you are using for top-off and water changes is free of phosphate and other impurities.

D-D H2Ocean Magnesium Pro PLUS Saltwater Mixing Kit

Water changes are one of the best ways to remove phosphates already present in your system. Removing the phosphate-filled water and replacing it with clean, pure saltwater can make a dramatic difference. Staying regular with your aquarium maintenance schedule and changing 5-10% of your system’s total water volume every 1-2 weeks will help you combat the problem.

protein skimmer will help remove phosphate while it is in its organic form. An efficient skimmer removes protein and organic waste before they can break down inside your aquarium. Our most popular protein skimmer brands this year are AquaMaxx and Reef Octopus, although for smaller tanks, you may want to check out the AquaticLife Internal Mini Protein Skimmer 115Tunze Nano DOC Protein Skimmer 9002 or Hydor Koralia Nano/Slim-Skim.

To actively and specifically remove phosphate from your aquarium, a reactor filled with phosphate-removal media is the most effective method. Two Little Fishies GFO Phosban Reactor is a great economical reactor, although the AquaMaxx GFO and Carbon Filter Media Reactor is an excellent high-quality alternative built using better materials. Fill the aforementioned reactors with granular ferrous oxide (GFO) filter media, such as AquaMaxx Phosphate Out or D-D ROWAphos, to bring your phosphate level down to zero. Read How to Setup a Media Reactor and watch the accompanying video to help get you started.

A biopellet reactor is another piece of equipment aquarium keepers can use to remove phosphate from their tanks. Biopellet reactors remove both nitrate and phosphate and may be used in conjunction with a phosphate reactor. AquaMaxx BioPellet Reactors and Hydra Aquatics BioPellet Reactors are each available in two sizes and help initiate a more efficient denitrification process. To learn more about biopellet reactors, read Setting up a Biopellet Reactor.

Liquid additives can also be used to lower phosphate levels in your aquarium. There are plenty of well-reviewed phosphate removers on our website, with Blue Life Phosphate Rx garnering the most reviews. You can also try a nitrate & phosphate reducer, like long-time favorite Korallin PO4 Minus. Red Sea NO3:PO4-X Nitrate & Phosphate Reducer has been a popular choice this year. Additives are more economical for small aquariums or for intermittent use since no additional equipment is required.

For a natural and supplemental phosphate removal method, growing and harvesting macro algae is a popular option and can be very effective. Macro algae (typically Chaetomorpha sp. or Caulerpa sp.) is grown in a lighted refugium. The macro alga consumes phosphate, nitrate and other organics as it grows and is exported by trimming/removing the macro algae. Along with nutrient export, another benefit of a refugium is that it is a place where microorganisms (such as copepods and amphipods) can reproduce without being eaten by fish or coral. As the microorganisms reproduce, many will find their way into your display tank to provide a natural live food source for tank inhabitants. Read How to Setup a Refugium and Refugiums: An Overview and Some FAQs to learn more.

Some hobbyists have reported nuisance algae growth even though nitrate and phosphate levels are undetectable. This often results from organic phosphates bonding to live rock or live sand. The most common cause is trapped detritus due to poor water circulation, unclean/unchanged mechanical filtration or old live rock/sand.

In the aforementioned scenarios, there is an overabundance of bonded organic phosphates. As the organic phosphate slowly converts into orthophosphates, it becomes food for algae. Phosphate test kits won’t detect the presence of orthophosphate because it is quickly consumed by the nuisance algae. The solution is to remove as much of the detritus as possible, either by rinsing the live rock in a bucket of saltwater outside of the aquarium or by blowing out as much of the trapped detritus as possible with a powerhead during water changes to remove the trapped detritus. In addition to removing the detritus, you will need to continue a phosphate removal regimen to remove as much of the orthophosphates as possible. Over time, the algae problem should disappear.

With the various methods of phosphate control described in this article, any aquarist should be able to keep their phosphate levels in check to curb nuisance algae growth. Of course, if you have questions, please don’t hesitate to contact us! Tech support is always free and we’d love to learn more about you and your tank.

We use cookies to provide a personalized site experience. By continuing to use & browse this site, you agree to our Privacy Policy.