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Cyanobacteria Problems

I have a cyanobacterial growth in my saltwater aquarium. Is it Bryopsis?

By J. Charles Delbeek

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Q. Would you please help identify this algae in the photos I’ve sent? (Photos are not shown here. —Eds.) I think it may be Bryopsis. All water parameters are within specs, except nitrates at about 10 ppm. I am also having trouble getting the pH up to 8.0 or above. I added crushed coral to the substrate of “Arag-Alive” Fiji pink live sand, but the pH still won’t reach above 7.6. When I first set up this saltwater aquarium about six months ago, I added some live rock.
Michael D. Cregar

A. The pictures you sent show some cyanobacterial growth, but not Bryopsis (a green fluffy algae resembling a bundle of featherlike tufts that can reach a couple inches long).

Cyanobacteria appear when nutrient levels become elevated, especially phosphate. It is not uncommon to have growth of cyanobacteria when an aquarium is first established, because nutrient levels can become elevated in the beginning, particularly when using new live rock. You don’t mention anything about filtration, lighting or aquarium management practices, so it really is impossible to troubleshoot your system.

Is this a reef aquarium with corals or a saltwater aquarium with just live rock and saltwater fish? If you do not already have one, I urge you to purchase a protein skimmer. These remove a large number of compounds from the water and have a positive impact on water quality. I would also take a look at the quality of freshwater you use to replace evaporation and mix new saltwater, because the source water can sometimes have elevated levels of phosphate and nitrate, as well as other plant/algae nutrients.

You should be measuring calcium and alkalinity levels, because these are closely tied for maintaining pH. Adding crushed coral will do little to raise the pH much above 7.8 or so; its main role is to act as a buffer against pH that is too low. If you use a test kit to measure pH, you might want to buy fresh reagents to ensure a correct reading. If using a pH probe and meter (the recommended method, usually available for less than $90), make sure the probe is less than 2 years old and has been calibrated recently.

You should do several things to raise pH. First, get alkalinity into the range of 2.3 to 3.5 meq/L through the addition of buffering compounds. This will help reduce fluctuations in pH over the course of the day. The buffer will also contain compounds that will help raise the pH.

Second, make a solution of calcium hydroxide and water (kalkwasser) to replace water lost via evaporation. This will have a high pH that can help reduce phosphate, will aid in the conversion of carbon dioxide into bicarbonates (which will help to boost alkalinity) and will neutralize acids produced by biological activity in your aquarium, thus raising pH.

If the levels are correct for alkalinity and calcium, and you are using a protein skimmer but still have low pH, then this may be a sign of excess carbon dioxide in the water, which acts to lower pH. This could be due to poor air ventilation in the room, a tight-fitting aquarium cover or the aquarium being in a crowded room. One way to test this is to place an air stone in the aquarium, and aerate the water vigorously. If the pH begins to rise in just a few hours, it’s a good sign there is a carbon dioxide problem.

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