Unable to reduce phosphate with Seachem Phosguard and Chemipure Blue


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I've got a 50 gallons reef tank, with LPS and Softies that's been running for about 7 years. It's gone through all the ups and downs of GHA, Diatoms, Dinos and Cyano in the past. The tank is not having any of those issues anymore.

Tank parameters:
Ca: 410
Mg: 1320
Kh: 8.9
Nitrates: 10 ppm
Phosphates: 0.25 ppm

The water and the rocks are clear and the corals are fine. But I think they can be better. I'm trying to bring the phosphates down to around 0.05 to see if it brings out more color and growth in corals. But I'm just not able to.

I dose NoPox for nutrient control. And we know that works better on nitrates than phosphates. So, to bring down the phosphates, I added Chemipure Blue in a Reef Octopus reactor and also Seachem Phosguard with a separator on top of it. I've made sure the water is pushing through the media gently without tumbling them.

So far, I've finished a 250ml bottle of Phosguard replacing it every four days as per the instructions. And now I'm on my second bottle. My phosphates still read 0.25ppm. Apparently, even Chemipure Blue hasn't done its part to reduce the phosphates.

So, I tested the water coming out of the media reactor and was hoping for a low phosphates reading. And to my surprise, I got same reading of 0.25ppm. I then tested my RO water to see if my test kit is fine. And I got a proper reading of 0ppm.

I've read so many reviews and feedbacks about the effectiveness of these two products to bring down the phosphates. I'm just baffled why it's not working at all for me. It's been three weeks so far trying these two products.

Can anyone chime in from experience what am I doing wrong?

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Unfortunately, I've got only RO unit. But how can that interfere with removal of phosphates with these media?

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I guess I've figured this out a little, and thought I'll update this post with my experience.

Well, first of all I would like to clarify that these products do work. But then, their effectiveness depends on age of your tank and whether it's the first time you're bringing down Phosphates to very low levels.

All the information I share below is anecdotal without scientific evidence, but eventually, I was able to bring the phosphates down and I'm sharing what I believe may have happened.

I've mostly had LPS Corals that can tolerate slightly higher phosphates. Hence, I never bothered to bring it very low. So, my tank was running with high phosphates for many years. And it seems that in such tanks, phosphates are much higher than what we test with the water. It seems to be true that phosphates get bound in the live rock, substrate or other biomedia materials in the sump. These are not read by our test kits. So, what happens is that when we use Seachem Phosguard or Rowaphos products to take out the phosphates from the water column, the equilibrium of phosphates between the water and LiveRock/Substrate/BioMedia is disturbed. And to restore the balance, phosphates are leached from LiveRock/Substrate into the water. Hence, initially you may feel like Phosphates are not coming down as you can't see it reduce with test kits, but in reality they indeed are being taken out from the water. However, I felt like the amount of Phosguard I was using was not able to keep up with the daily phosphates added by fish and coral food plus the phosphates being released from LiveRock/Substrate. In order to bring down the overall phosphates in the tank, I had to ensure that I'm taking it out faster from the water than the what's being added back into it. I was gradually increasing the amount of Phosguard I'm using, but it wasn't making much difference. I thought this will go on forever and phoshphates may not even budge.

So, I went ahead and used an entire 250ml bottle of Phosguard on my 50 Gallon Reef tank in one go. And I was finally able to bring the phosphates noticeably down, but still not low enough to my desired level. So, I replaced the media again with another big portion of 250ml of "Phosguard" after 4 or 5 days and simultaneously added another product called "Fauna Marin Phos 0.04" to provide additional help. However, I added Fauna Marin product at recommended quantity for 50 Gallons reef tank. And as the levels kept dropping, I reduced the quantity of Phosguard to 150ml, and eventually to 100ml. Whereas "Fauna Marin Phos 0.04" was left in the media reactor for 2 weeks.

In other words, I was throwing in probably 3 times the recommended quantity of products to remove phosphates in my tank to bring them down. And if the other reefers are true about these products effectiveness, then the only possible explanation is that, indeed I had a lot of Phosphates bound in my tank that was not in water column.

But it doesn't end here...

When I was finally able to bring the phosphates down to 0.05 ppm, I started seeing small strands of Dinoflagellates. I'm glad I caught it immediately before it takes over the tank. I know this can happen with low nutrient tanks when the population of good bacteria could be low and these pesky things try to take advantage and overgrow. Anyways, I did a 3 days light out, while simultaneously running UV Sterilizer in a closed loop to circulate the display tank water through it and back into the display tank. During this time I stopped Carbon dosing and let the Nitrate rise up a little. Three days later, my Phosphates reading jumped back to 0.25 ppm!!

This proved that a lot of Phosphates were not just bound by LiveRock/Substrate, but another big chunk was in the micro organisms that are in the water and could multiply to very high levels in the water without us noticing it as we don't see them; until they become astronomically high and become visible with our eyes as bacteria or algae blooms. And because of the UV, they were sterilized and may have release the Phosphates back into the water.

So, I had to redo the process. But this time I used recommended quantities of Phosguard along with recommended quantity of Fauna Marin product. So, that's twice the recommended capacity overall. The phosphates dropped better than before at the same quantity. I suppose, that's probably because the LiveRocks and Substrates were not having enough Phosphates bound up anymore. Another few days passed bringing them down to the desired levels of 0.05 ppm. The UV Sterilizer was running throughout the time. And I'm glad there are no signs of Dinos. And all corals look fine. Now, I'm ready to take it to the next step and see how I can make the corals look better.

So, here's my conclusion.

In aquariums where Phosphates have been let to stay high for many months or years, you can dose more than the recommended dosage of the media to gradually drop phosphates. How much more will depend on the system.

I would advise to start with recommended dose, wait 3 or 4 days to test the readings. And if nothing changes, replace the media (coz it's probably exhausted by now) with double the quantity. Test again after 3 or 4 days. Keep on doubling the media with every change until you finally notice the readings drop. And then, you gradually reduce the quantity of the media during the next change based on how fast it reduces from that point onwards and how fast you want to bring it down. Once, you see that the phosphates are coming down, I would recommend reaching your target level slowly over a period 3 or 4 weeks.

And if you're not using UV Sterilizer, you probably still have a lot of Phosphates bound up in microorganisms. And not all of it can be skimmed out. Anyways, use of UV Sterilizer is another topic by itself and I won't say more on that here.

A couple of bonus tips.
Make sure your media reactors are pumping water at manufacturer's recommended level to give enough time for the water to interact with the media to reduce the phosphates, but not too slow that it only treats a very small quantity of your tank's water per hour.
For some unknown reason, Phosguard is not so effective for me when I use it in a Media Reactor. However, when I place it using a media bag in the sump chambers such that all the water passes through it to reach the next chamber, it works at its best.

Hope this helps someone who's struggling to bring down Phosphates in their tanks.
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