High Phosphates in Reef Aquarium

Dealing with high phosphates in reef aquariums is something that every marine hobbyist will have to address.  There are many ways to handle high phosphates such as frequent water changes, GFO, Chateo algae in the sump, and my favorite to date is algae scrubbers (read about algae Scrubbers on Corallore). However this article is not specifically about how to lower your high phosphates since that has been discussed many times through forums and articles on the internet and books.  This article goes over the important steps you need to take to protect your reef inhabitants while you have high phosphates so they do not die.

Green Montipora cap browned out during phosphate spike
Green Montipora cap browned out during phosphate spike

Whenever you realize you have high phosphates in your aquarium I think the first and most obvious step is to start with a large water change.  Get some clean water circulating through your system.  The next step I recommend is to dial in your protein skimmer to skim more heavy or “wet”.  It’s possible if you have high phosphates you weren’t skimming enough to begin with.

The third step and one I actually recently learned of myself is adjusting your lighting period during high phosphates.  It was pointed out to me in another forum and using his advice my SPS made a very rapid recovery in just a few weeks instead of the few months I had anticipated.


If you are a frequent reader of my posts you will know that I had recently added an algae scrubber to a heavily fed reef tank. Heavily feeding the tank causes high nitrates and high phosphates.  I do not want to spend a lot of money on constant water changes so I installed a large algae scrubber.  An unexpected side effect of the algae scrubber was that as algae was transferred from the tank to the scrubber it made my phosphates spike for a short time.  I attribute this to a quick die off of tank algae releasing phosphates into the water.

Here is a picture of a green Montipora cap one month before the high phosphates in the reef aquarium.

Green Cap 10-16-2012
Green Cap 10-16-2012

Once the high phosphate spike was underway the Green Montipora Cap turned a dark brown. This was not a one month transition to this color, it happened practically over night, i just didn’t have a picture from the previous day.

Green Montipora cap browned out during phosphate spike 11-16-2012
Green Montipora cap browned out during phosphate spike 11-16-2012

Having been a marine hobbyist for many years I have experienced phosphate spikes before and generally corals are sadly lost and the ones which survive take a few months to fully bounce back to their former beauty.

The browning of this particular Montipora was almost an overnight transition which was incredibly fast.  This indicated to me that it wasn’t the normal browning you get from low light or the slow browning you get from to many nutrients in water, something else was going on.  Which lead me to forums to maybe see if there was something I had missed, that’s when I had gotten this piece of advice from a fellow reefer and I cannot thank him enough so I thought I would pass the tip along.

“P04 causes a coral to become photo-inhibited, which in turns makes it more sensitive to light and prone to bleaching, browning, and dying under normal reef lighting conditions. You might consider either shortening the photoperiod a bit further, or if possible, lower the intensity until you get your phosphates down.”

I adjusted my lighting schedule to be six hours and less intense instead of the 9 hours at one hundred percent.  My algae scrubber, skimmer, and water changes quickly had the spike under control and to my surprise the coral color immediately started to change back to green.  Had I kept the lighting period and intensity the same the corals would of continued to struggle for longer causing the recovery to be slower.  Over the course of two weeks I gradually ramped the lighting period back to what it previously was and no corals were lost.

Less than one month later the montipora cap has returned to its former color and everything is fine.

Green Monticap fully recovered 12-05-2012. (sorry for so much actinic in this pic)
Green Monticap fully recovered 12-05-2012. (sorry for so much actinic in this pic)

To recap the steps so far I have found most important to take during a high phosphate spike:

  1. Frequent and large water changes
  2. Dial in your protein skimmer to skim wetter.
  3. Dial down your lighting period during the phosphate spike.


Hopefully using these steps you will not experience any coral loss and your recovery period will be short and you will be back to enjoying your beautiful reef as fast as possible!





8 thoughts on “High Phosphates in Reef Aquarium

  1. Have you had any issues with nitrate/phosphate balance since implementing the scrubber. I find my scrubber is nitrate limited, I tend to need to run GFO periodically otherwise I get a buildup of phosphates in my system.

    1. Hi Justin,
      How long have you been running your scrubber? I run nothing else besides my scrubber and my skimmer very wet and it manages my phosphate levels just fine even with very heavy feedings.
      It did take about two months though to see the scrubber doing a good job of this. I also have found there is a balance you have to keep with the algae scrubber to keep your phosphate levels low. If you clean your scrubber too much or too soon there is not enough algae to keep your phosphate levels under control. If you do not clean it often enough some algae will break loose of the scrubber and decompose in your system causing the phosphates to be released back into the water. I hope this helps a little bit.
      Thanks for the comment.

  2. Hi I have a veru high phosphate reading and have been doing loads of water changes, skimmer is on over load, oh and I have had this tank 3 weeks after collecting it setup and moving it on a two hour drive, everything accept 3 fish survived. I didn’t clean the sump out thoroughly as i needed it to start working but did leave it over night to settle and since have struggled with my phosphate levels, I have purchased phosphate remover and put that in my sump but not seen much change over 4 days 🙁 replaced over half the tanks water ???? Help

    1. Hi Nikki,
      Besides seeing the phos levels being up are all the animals currently healthy? Do you have a lot of algae? I wouldn’t start dumping a lot of chemicals in the water for phosphate removal. After moving a tank I would expect a spike in phos and nitrates and another mini cycle. I would keep doing small 10% water changes every few days and let it run its course. You could run some GFO if you have the equipment to do so, and that would give you some stress relief.

  3. R X phosphate remover that’s all I have to say. This stuff works amazingly, I have high phosphates green algae growth and in one day I see no difference period anybody with my classmates have got to try this.

    1. Sorry for my last comment it was a little messed up first time on this blog. But what I want to say is that I did see a difference in my algae growth in one day and anybody that has hi phosphate has got to try R X it’s an amazing product.

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