Reef Tank Phosphates: Easy Ways to Reduce Them!

Phosphate is an important but often overlooked parameter in a saltwater aquarium. High levels of phosphate can prevent the skeletal growth of coral and fuel horrendous algae blooms!

I had no idea about phosphate until my corals were not growing and a fellow reefer asked me what my phosphate level was! From that point on I soon found out how phosphate affected my aquarium!

Aquarium Phosphates are best controlled using high-quality filtered water, reduced feeding & fish stocking, regular maintenance & detritus removal, and even some chemical removal products. Phosphate should be kept under 0.50ppm for fish only, 0.05ppm for LPS & Soft corals, & 0.03ppm for SPS corals.

The best way to combat high levels of phosphate is a multi-angled approach after you have decided what the maximum level of phosphate can be tolerated by the type of aquarium you own.

  • For Fish-Only aquariums a maximum of 0.50ppm
  • For LPS, Zoas, and Soft Corals a maximum of 0.05ppm
  • For SPS dominant aquariums a maximum of 0.03ppm

Be advised that you will need SOME phosphate in your aquarium to be used by your corals to grow, so going overboard and completely stripping your water of phosphate will have the same effect of slow coral growth as having too much! The key is to find a balance for your system, as everyone’s is different!

Now we have the limits recommended by the hobby in mind lets look at what phosphate is, where it comes from, how it affects the tank, and how to manage it. If this interests you then please read on!

What Are Ways To Lower Phosphate In An Aquarium?

There are four main ways to help lower the Phosphate level in your aquarium:

1. Water Changes & Vacuuming of Sand Bed (Detritus Removal)

As explained earlier, your aquarium is an enclosed bio-system that will build up Phosphates over time. Each time you complete a water change you are physically removing Phosphates, and if you are replacing that water with RO/DI filtered water, your Phosphate level will reduce over time.

More Out, Than More In = Reducing Level of Phosphate!

The other aspects associated with a water change are vacuuming the sand bed to remove uneaten food, decaying matter, and detritus and scraping your glass. By doing these two tasks you are getting the Phosphate laden material into the water column and removed, thus lowering your Phosphate levels.

2. A Good Protein Skimmer

A correctly sized, clean and efficiently working protein skimmer is another great way to help keep Phosphates low. The skimmer’s job is to remove Dissolved Organic Waste. Waste, as we know, breaks down and releases the phosphate bound up within it.

By allowing your skimmer to move this waste into the collection cup and then emptying that cup, you have now removed that material before it has a chance to release the Phosphates into the water.

3. Macro-Algae in a Refugium or Turf Algae Scrubber

Algae is a wonderful consumer of Phosphate and if you can spare the room, adding a Refugium and/or possibly an Algae Turf Scrubber to your system will greatly improve your Phosphate reduction.

Growing Macro-Algae in a Refugium and then physically removing half the mass as it grows instantly removes the phosphate that is bound up in the algae. This process also helps to remove Nitrates at the same time.

There are many benefits to having a Refugium on your system and you can learn more about them in my Refugium Article which you can find HERE

The other excellent device you could look at implementing is the Algae Turf Scrubber. This device cascades your aquarium water down a plastic mesh which is lit by a ‘Plant Growth’ bulb. As the algae grows, it consumes Phosphates and Nitrates which you then remove, clean the mesh, and put back into service. As the algae grows again, it consumes more Phosphate and Nitrate. Rinse and Repeat as the saying goes!

Algae Turf Scrubber
DIY Algae Turf Scrubber Mesh

If you wish to find out more on Algae Turf Scrubbers please check out my article on them HERE. This is one of the next products on my list to fit to my system – I just have to find the room!

4. Chemical Absorption Products

Granular Ferric Oxide (GFO)

This is a product very popular for long-term Phosphate control. Most aquarists use this at an early point in the life of their aquarium after using other products to lower the Phosphate to the desired level.

Think of GFO as a maintainer type of product.

It works by absorbing the Phosphate compound and chemically binding it to the Ferric Oxide. As your mass of GFO becomes used up the phosphate level will begin to rise. It is at this point you remove the GFO media, dispose of it and replace it with new.

GFO is prone to clumping so the most efficient way to implement GFO is in a reactor which allows the granules to ‘Bubble’ as the water flows through it. Once GFO is used for long term maintenance, it can last 1-3 months between changes, depending on your Phosphate level.

Aluminum Oxide

This is another common product and it is mainly used for rapid Phosphate removal. You have to be careful using this product, as with any rapid change in water chemistry, you can send your aquarium into shock and cause your tank to crash. This product also absorbs the Phosphate compound and binds it to the Aluminum Oxide, but rapidly. Usually, this product will need to be replaced weekly.

Aluminum Oxide does not clump together like GFO so it can be placed into a mesh bag and added into your sump or aquarium until it has lowered your Phosphate to the required level.

This product is used more to lower your Phosphate then GFO will be used to maintain that desired level.

Liquid Phosphate Removers

Products such as Blue Life Phosphate Rx, Brightwell Phosphate-E and Ultralife Reef Liquid Phosphate Remover chemically attract and bind the Phosphate and precipitate it out of the water.

This is where it allows the liquid binding agent and its attached phosphate compound to come out of dissolved form and become a solid, at which point your protein skimmer and filtration media will collect it ready for removal by you.

Liquid Phosphate Removers

Most of the liquid removers work best when added to the area in which your protein skimmer is located. As the liquid binds your phosphate it will instantly be removed. Any liquid that doesn’t make it straight into the skimmer will be caught and removed later.

What Are Phosphates In The Aquarium?

Phosphates are one form of the Phosphor compound. They are an organic salt and they are found in all living things. Your aquarium is an enclosed eco-system and your levels of Phosphate will slowly build over time if you do nothing to remove them.

How Do Phosphates Effect my Aquarium?

By allowing them to build to levels higher than those recommended for your type of aquarium they can begin to affect your coral growth and increase the amount of algae you see in the tank.

Coral Growth

Once phosphate begins to reach levels above 0.05ppm is begins to inhibit the precipitation of calcium carbonate from the water. When a coral like Acropora or Torches, for instance, wish to build their skeletons they consume calcium carbonate from the water as one of the main building blocks.

Coral Frags
My SPS are growing well now!

When phosphate levels begin to inhibit this uptake of calcium carbonate the coral stops growing and can even die if it is unable to consume enough calcium carbonate from its surrounding environment.

This was what was happening to me. My phosphate was at 0.1ppm which didn’t seem high, but it was enough to make my corals grow at a snail’s pace!

Algae Growth

Phosphates are loved by plant-based organisms and when it is available in high enough quantity in our aquariums they can fuel rapid and sometimes fatal algal blooms. Not only do the algae blooms look hideous and can be a major battle to overcome they can smother coral to the point of death.

Luckily for us, we can use algae’s love for phosphates to our advantage by growing and disposing of algae in a Refugium or Algae Turf Scrubber. Keep reading to find out more about these superb additions to an aquarium!

If you find you are having excessive algae growth and your corals seem to be growing slowly, you may be starting to see which parameter you need to test for!

Where Does Phosphate Come From In An Aquarium?

There are three main sources of introduction into our aquariums:

1. Fish Waste/Detritus

Fish waste and dead or decaying matter will all release Phosphate into the water. As these items break down, they release the Phosphate that is bound up inside them into the water column.

The more fish you have in your aquarium, the more excrement and detritus you will have, therefore the more your maintenance and phosphate management techniques have to deal with to prevent the Phosphate level from rising above the acceptable limit for your type of aquarium.

2. Fish Food and Over-Feeding

Fish food, especially flake food, has always been known to be high in Phosphate. Over-feeding is a sure way to having your Phosphate level begin to increase. Just as waste and detritus above, any uneaten food begins to break down and it releases its trapped phosphates into the water.

3. Poor Quality Fresh Water, High in TDS (Total Dissolved Solids)

Unfiltered city or well water is usually the main culprit for introducing Phosphates into your aquarium. The use of a maintained and high-quality RO/DI water filter system will ensure you have water with 0 TDS for use when adding ANY water to your aquarium, be it via the Auto Top-Off System or when making a new batch of saltwater for your water changes or the initial aquarium fill.

TBR Recommends

Marine Depot 4 Stage Advanced RO/DI System

A Good Quality RO/DI Water Filter Help Will Prevent So Many Water Problems!

What To Be Aware Of When Lowering Phosphate In An Aquarium

Some phosphate removal products can rapidly remove/lower your phosphate. This sudden change can shock your aquarium inhabitants. Test your water, see what your Phosphate level is, decide how much you want to lower phosphate by for this week, then dose accordingly. Slowly repeat until you have your desired phosphate level. Then use GFO to maintain that level.

The maximum recommended rate for Phosphate removal is no more the 1ppm per day, especially if your aquarium has had a high phosphate level for more than a few weeks.

Take your time and allow the phosphate level to gradually reduce and allow your bio-system time to change to the reducing levels.

How Do You Test For Phosphate In Aquariums?

In my opinion and that of many other experienced aquarists there is only one true test kit: The Hanna Phosphate Checker Series

Select the Checker that matches your phosphate level. Each Checker measures to a specific range of Phosphate.

The Hanna HI713 LR (Low Range) Phosphate Checker is best used for Freshwater or Fish Only aquariums where the Phosphate levels being tested for can be higher. The LR checker is not able to test low enough for any aquarist keeping corals, especially LPS and SPS.

This Checker measures in the 0 to 2.50ppm range

Hanna HI774 ULR (Ultra Low Range) Phosphate Checker is used to test for the absolute lowest level of Phosphate in your aquarium. When your level is too low for the LR tester, this Checker measures down into the very low range allowing you to test for even the smallest traces of Phosphate. This is a great device for the experienced SPS keeper who wants to keep their Phosphate at a very accurate and low level.

This Checker measures in the 0 to 0.9ppm range

All of these testers use the Orthophosphate Analysis Method which is a way to test for Phosphates without using a prepared sample involving a digestion acid. The Hanna checkers use a combination of an Ascorbic Acid, an LED light source and a Silicon Light Detector to provide you with a simple, accurate and easy-to-use tester.

Most of the other test kits on the market are unable to test in a range low enough to be of any use to coral keepers.

==> You can view the range of Hanna Checkers HERE at <==

To Finish

The key to keeping Phosphates low is a multi-angled approach. Good aquarium maintenance, quality water filtration, and a low aquarium bio-load will keep your phosphates low.

Maintaining this by using a product like GFO will see you well on your way to rapidly growing, colorful and healthy corals.

Further Reading

Some of my other articles you may find helpful:

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Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

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