Diatomaceous Algae Taking Over Your Saltwater Aquarium?

A couple of years ago, one of my saltwater aquariums developed a serious problem with diatomaceous algae.

This dreaded ‘brown monster’ has been a bane to many a reefkeeper. Diatomaceous algae, when rampant, has caused many saltwater aquarium enthusiasts to tear down their tanks and leave the hobby. Attempting to control it is extremely frustrating and seemingly futile. Watching it smother your corals and live rock in a layer of brown is downright heartbreaking! May this article give hope to anybody battling diatomaceous algae or problem algae of any type.

diatomaceous algae

Recovering from diatomaceous algae

I started my second saltwater aquarium — a 3′ x 2′ x 2′ — in April 2006. After running my first tank, a two-and-a half-foot, 30 gallon since 2005, I felt the need to upgrade. After 6 weeks of cycling the new tank, I transferred all the fish, coral and live rock from the 30 gallon. I was always cautious about overfeeding the two fish in my 30 gallon– a yellow-tail damsel and a maroon clown — and experienced no algae problems whatsoever in the year and a half I had it.

But I became guilty of overfeeding my new tank. I dosed nitrate-inducing supplements like Marc Weiss ComboVital almost daily seeing as how my corals were opening up nicely. I was also feeding my fish pellets, frozen mysis, flake food and Cyclopeeze three times a day. All my LPS corals were plump, fat and growing and little orange-feathered coco worms were multiplying in nooks and crannies everywhere!

I reasoned that I had 100 gallons of water and also 100 pounds of live rock as my tank’s biofilter and that it would take care of any elevation of nitrate should it occur.

But I was mistaken. My aquarium’s biofilter was yet too immature to handle the multiple feedings. I had also stopped testing for water quality since everything appeared to be ‘fine’.

It all started with innocuous looking little tufts of brown diatomaceous algae started to grow on the live rock. Pretty soon, they started overtaking the purple coralline algae and also smothering some of my corals. My saltwater aquarium was in huge trouble with no easy answer in sight.

A check with the test kit revealed that my nitrates had skyrocketed to 100ppm or more. Nitrates were obviously feeding the explosion of diatomaceous algae. I needed to address the elevated nitrates right away.

I started by changing 10 gallons of saltwater every 3 days, siphoning out as much of the brown algae off the rock as I could, filling 5-gallon pails with the algae that came off. But all seemed futile, as it grew back in 2 days.

My phosphates at this point were reading at 0.03 ppm on the exam kit. I figured phosphate was being taken up by the diatomaceous algae as swiftly as it was being produced, resulting in a lower readings than I thought. I changed out the Rowaphos weekly, soon using up a 500ml pack.

After the Rowaphos ran out I decided to try PhosBan, another brand of phosphate reducing media. PhosBan has a finer particle size than Rowaphos and as it tumbled in the fluidized reactor, it somehow managed to grind itself up to a fine powder, releasing itself into the sump. A lot of the Phosban also made its way up the return pump adding yet another brown hue to the main display. Thing’s just got worse.

And the algae still would not budge.

By now, I realized that phosphate was leaching from the live rock, fuelling the algae along with the high nitrates.

After three months of contesting the brown monster — with several empty cans of Rowaphos lining the wall in my fishroom like grim trophies — the tide started to turn. The live rock began to look grey once more. Little tufts of brown algae stayed yet they weren’t spreading all over the rock.

Once pink coralline started appearing in the fifth month, I started to replace the corals I had lost. And slowly, over a few more months, my tank started to regain its former glory.

So what did I learn from all of this?

  • Water changes are important but not the total solution when battling problem algae. A good phosphate remover is really the key. Use water changes as an opportunity to siphon out as much algae as you can.
  • Phosphate can be bound up in the rocks and leach back into the water over time. This is a very good reason to run phosphate remover from day 1 of your aquarium’s life
  • Run phosphate removing media in a phosphate reactor 24/7 and test the water coming of the reactor. Change the media once the reading is greater than zero.
  • Do not quit. With patience and perseverance, you can win the battle against nuisance algae!

Read more about Nuisance Algae and Preventive Aquarium Maintenance:

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