Think about how many times you’ve heard people talk about keeping your phosphates
low in your tank.
Then go look at all the various phosphate-removing medias on the market.
Any local fish store or online retailer will have several offerings for products that claim
to remove phosphates from your tank.
It seems that everyone is phosphate crazy!
Why is everyone so phosphate crazy?
To understand why, you have to first understand more about phosphates.
In your saltwater tank, phosphates mainly occur in 2 main forms:
- Soluble Reactive Phosphates (SRP)
- Organic Phosphates
SRP is an inorganic form of phosphate. In everyday language, that means that SRP is a
simple form of phosphate that is dissolved in your tank’s water and easily used by algae
and bacteria. While this might be the first time you’ve heard of SRPs, you’ve actually
been giving SRPs a lot of attention!
You’re probably saying to yourself,
“When in the heck have I ever paid attention to SRPs?!”
Here’s when:
Whenever you run a phosphate test on your tank, you are measuring SRPs.
In fact, without really expensive scientific gear, SRPs are the only phosphates you can
measure in your tank.
Therefore, given that SRPs are used by algae and are the only kind you can easily
measure, it makes sense that you and everyone else give them so much attention! They
are the source of all your algae problems…right?
Wrong.
We hate to be the bearer of bad news, but we have to tell you that SRPs may account for
less than 2% of all the phosphates in your tank. That means you are giving a lot of
attention to something that isn’t overly prevalent in your tank!
SRPs are important however, and we’ll dive more into them in a later chapter. For now,
understand what they are – phosphates that are dissolved in your tank’s water - and that
you’ve only been testing for SRPs when you run a phosphate test.
The other main form of phosphates in your tank is organic phosphates.
Organic phosphates are phosphates that are bound to
or incorporated in organic material, instead of being
soluble in the water like the SRPs. Imagine a brick
wall that is made up of lots of red bricks and just a
few green bricks. The green bricks are phosphates
and the red bricks are organic matter. So as long as
the green bricks are part of the brick wall, they are
bound to the red bricks and can’t be easily removed.
If we told you to remove a single green brick,
you’d have to do a lot of work to extract just one green brick.
That means organic phosphates are more complex and harder to breakdown than SRPs, as
the organic phosphates first have to be removed from the organic matter (in our case, the
brick wall) before they can be removed from your tank. Also, since organic phosphates
are part of the organic material, that means you can’t test for them in your tank because
your test kit only measures phosphates dissolved in your tank’s water (hint: SRPs). Given
that fact, you now understand why your phosphate test kit only measures SRPs! This fact
also shows you that counting on your test kit as an overall measure of phosphates in your
tank is horribly inaccurate.
You can measure organic phosphates, but not without really expensive and fancy
equipment that most aquarists don’t have and likely won’t be willing to purchase.
We’ll come back to organic phosphates later. For now, know that they are much more
prevalent than SRPs, and that you can’t easily test for organic phosphates.
Make no mistake, phosphates cannot be ignored in a saltwater tank, especially when it
comes to battling nuisance algae. If you have phosphates, you’ve something that algae
need (and badly want) to grow. No wonder everyone is phosphate crazy!
Can we really blame them though? Nuisance algae are just what the name says – a
nuisance. It looks horrible even though your non-saltwater tank friends will look at your
algae-infested tank and say, “It’s so pretty!”
As saltwater tank hobbyists, we hate nuisance algae and phosphates and we’ll go to great
lengths to keep them out of our tanks. However, the thought of never having any
phosphates in your tank is futile.
The tank is closed, so how did all this phosphate get in here?!
One of the most frustrating parts of owning a saltwater tank is wondering how things like
algae can suddenly appear in your tank when you didn’t deliberately put them in there.
Phosphates seem to fall into the same category: One day you have zero phosphates in
your tank, and the next day, “WHAM!”
Phosphates show up!
So where did they come from if you aren’t dosing phosphates?
The answer: lots of places.
Any fish food will contain phosphates. And that’s not a bad thing. Your fish need
phosphates as part of their diet, so a fish food containing phosphates is doing its job.
The problem occurs when you feed so much food that your fish can’t eat it all. When
your fish don’t eat the food, it begins to break down in your tank, which can drive up
phosphate levels as well as nitrate levels. If you feed frequently, then you have a
constant source of phosphates going into your tank. Since your tank is a closed system
(nothing gets in or out of it unless you put it in, or take it out), the phosphates will
continue to build unless you do a water change, adding phosphate-removing media, or
algae start to grow and consume the phosphates.
We’re not encouraging you to NOT feed your fish. We just want you to be aware that
fish food is a double-edged sword. Your fish need food, and overloading your tank with
it is bad.
Add in the potentially tank-trashing activities such as feeding corals or dosing your tank
with phytoplankton, and you’ve got even more phosphates to go around.
Tap water can contain phosphates and yes, you have to fill your tank with water
somehow. How do you remove phosphates from the water going into your tank?
The answer: You purify it with a Reverse Osmosis and Deionization (RODI) filter.
Properly purified RODI water will contain zero phosphates, which means every time you
do a water change, or top off your tank to replace evaporated water, you won’t be
dumping phosphates into your tank. Remember that you are dealing with a closed
system, so if you are constantly putting in tap water with high phosphates, these
phosphates will build up in your tank and cause issues like algae outbreaks.
As mentioned before, organic phosphates are phosphates locked in organic matter, and
one of the biggest sources of organic matter in your tank is your live rock.
NOTE: Before someone draws a conclusion from the above statement, we’re NOT
saying the presence of organic matter means you have organic phosphates.
Due to its highly organic nature, live rock can be a great harbor for phosphates. Take for
example, rock that was in a tank that had persistently high phosphates. These phosphates
were likely used by algae in the tank; the excess phosphates had to go somewhere and the
rock made for a great home. Over time, the amount of phosphates in the rock increased
and when this rock is placed in a low-phosphate environment (i.e. your tank if you do
what we tell you to), then the phosphates want to leach out of the rock.
The bad news about high-phosphate rock is that you can’t look at the rock and tell if it
has a high phosphate content. There are some possible warning signs like algae covering
the rocks, but even that isn’t a 100% positive sign of high-phosphate rock.
Some people will say you can test the rock for phosphates by placing it in a bucket of 0
phosphate saltwater and see if the phosphates in the saltwater rise. The problem with this
approach is that there might be lots of live things (sponges, algae, other organic matter)
that are dying off which would lead to a false positive phosphate readings.
Therefore, how do you keep potentially high-phosphate rock out of your tank?
Before you swear off phosphates altogether, realize that some phosphates are needed for
coral and bacteria growth. If you truly had a tank 100% devoid of phosphates, life would
be sluggish at best.
A scientific theory called the “Redfield Ratio” suggests some amount of phosphates
should be maintained in a saltwater tank. The problem with this approach is aquarists
end up trying to chase a perfect phosphate ratio and oftentimes drive themselves nuts
trying to hit an exact number. Worse yet, they crash their tanks by constantly tweaking
levels trying to get the Ratio right.
