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Author Topic: Blue-Green Algae  (Read 8181 times)
« on: April 23, 2006, 12:54:18 PM »

So, you've got a case of blue-green cyanobacteria. This pest is characterized by its slimy texture and is easily dislodged in sheets. It's not the easiest algae to get rid of. Check out this link:

If nothing you read there helps, try this approach:

If after a few weeks of big water changes and vacuuming up the BGA, you still can't erradicate it, here's plan B.

Day 1. Add 2.5 mg/L Maracyn.

Day 2. Add 2.5 mg/L Maracyn.

Day 3. You should now see a lot of dead BGA bacteria floating around in the tank. Do a big vacuuming to get rid of it.

Day 4. Most blue-green bacteria should be dead by now. Clean out as much as possible of the dead stuff. Use a jet stream of water from the outlet of a Python to remove it from plants and decorations. Let the filter work for a couple of hours then perform a 50% water change. Add 2.5 mg/L Maracyn.

Day 5-7. Wash the mechanical filter at least once a day. Keep a check on ammonia and nitrite readings but do not change any water unless absolutely necessary.

Day 8. Perform a 30% water change. Add 1 mg/L Maracyn.

From now on, resume your normal maintenance.

Here's some information on the use of erythromycin (Maracyn) to eradicate blue green bacteria. There seems to be a misconception in the hobby that erythromycin will negatively impact your biological filter. It in fact should not and here's why:


Bacteria can be divided into two groups, either Gram-negative (G-) or Gram-positive (G+). This classification is based on if the bacteria stains (+) or not (-) in a special staining technique - the Gram staining (invented by Christian Gram). Positive or negative staining reaction reflects a fundamental difference in the structure of the cell wall of the bacteria.

ERYTHROMYCIN IS AN ANTIBIOTIC. Erythromycin is more efficient towards G(+) bacteria than G(-). It is one of the safest antibiotics, meaning that it does not affect plants, fish or animals. Blue-green bacteria belongs to the G(-) bacteria but it is a special case with respect to sensitivity to antibiotics. They are more sensitive to erythromycin than other G(-) bacteria.

Fortunately, the bacteria important for the nitrogen cycle (your bio-filter) are of the G(-) type and are much less sensitive to erythromycin than the blue-green bacteria. So your biological filter is fairly safe.

The reason that some tanks experience an ammonia peak after treatment with erythromycin is (probably) not because the biological filter is non-functional. It is more likely that it is because of the high content of protein released from the dead blue-green bacteria which is broken down to ammonia and/or nitrite by the good nitrifying bacteria in your bio-filter. This boost of protein to be broken down upsets the finely tuned balance of different bacteria in your filter.
« Last Edit: July 30, 2006, 08:43:46 PM by JP » Logged
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