Tank Cycling & Bacteria Blooms


Bacteria Bloom, originally uploaded by attack11.

Bacteria blooms are caused by heterotrophic bacteria not the autotrophic nitrifying bacteria that are responsible for the cycling process.

Q: RM wrote:

Hi Christie,

I thought I’d give you an update as I’m still looking for some advice.

I have been making sure to put in enough Amquel and NovAqua to keep the ammonia levels at 0. I have yet to detect any Nitrite in the water, and the same goes for Nitrate’s. We’re around the 4 and a half week mark now. I realize that Nitrate’s take time so I’m being patient.

However, Odo’s fin rot has not gotten better. At first, it was only affecting his tail fin but now parts of his lower fin have began to fall off. He developed two holes in it and within 24 hours, the part of his fin between the holes was gone, as well as any of his fin which was on the outer part of the hole. The tail fin, while not being lost as quickly as before, is still ragged and slowly disappearing. I would say by this point, he has lost almost half of his tail fin. The plus side is that his appetite has not changed and he still seems as active as always.

About a week and a half ago, I put him on a 5 day cycle of Maracyn and Maracyn Two. This seemed to halt the fin rot but it has returned. Should I do another round?

One thing I have noticed is that the water has become somewhat cloudy, a white cloudy. I’ve read that this may be an indication of a bacterial bloom and it will eventually go away. However, this has been there for at least a week and a half to two weeks now. How concerned should I be?




A: There are a lot of different things going on in your tank to keep things nice and complicated. First, you are cycling, which of course is very stressful for even healthy fish much less one that is suffering from fin rot. Fortunately, the AmQuel and NovAqua will help to bind the ammonia and nitrite so they shouldn’t harm the fish. This is good for your Betta but bad for monitoring the cycling process. It’s almost impossible to know how close the tank is cycling because you can’t see the ammonia and nitrite spikes. If you stop adding the water conditioners, you put the fish at great risk.

Fin rot is also complicated. It’s a disease brought on usually by exposure to toxins like ammonia and nitrite, which make the betta susceptible to the bacteria that cause fin rot. Medications like Mardel’s Maracyn Two are great but if the cause isn’t fixed (poor water quality) the fish usually fall victim to the bacteria again. Even in a perfect world where the tank is completely cycled and the water parameters are spot on, fin rot can be very difficult to cure. New fin tissue is very fragile and it’s not uncommon to have relapses, sometimes numerous relapses.

The medication itself is the third major complication. Maracyn is really good fin rot medication and I have used it successfully many time in severe cases. In minor cases, consistently clean water is usually enough to promote fin growth. The reason Maracyn and Maracyn-Two work so well is because they kill the bacteria that cause fin rot. Remember though, antibiotics are pretty indiscriminant. They don’t know the difference between bad fin rot bacteria and good autotrophic cycling bacteria. If you treated Odo in the same tank you were cycling you may have wiped out many of the bacteria you have been trying to establish over the past 4 weeks. This is one of many reasons why aquarists keep a spare tank around as a hospital or quarantine tank. The bacteria bloom could be caused by several things but keep in mind that the autotrophic nitrifying bacteria (cycling bacteria) don’t cause bacteria blooms. Bacteria blooms are the result of heterotrophic bacteria and can occur at any time in cycled or uncycled tanks. These bacteria feed directly on organic compounds and tend to have blooms when we feed too much or stir up the sand or gravel (like after a siphoning.) Bacterial blooms can be difficult to pinpoint.

If you are worried that your Betta’s fin rot is becoming severe then I recommend keeping him in a spare tank with very clean water changed frequently while you continue to cycle the main aquarium using the fishless method. He’s been through a lot already with a tank cycling, fin rot and medication and he may benefit from some good ‘ol TLC in a clean, separate hospital tank for a few weeks.

I hope Odo feels better soon. Hang in there, the days of cycling that first tank can be a little stressful but really pay off in the end. To speed up things you may want to stop by your local fish store to ask them for a bag of used gravel. This will seed the tank with bacteria and will speed the cycling process up considerably.

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Christie F is a Betta splendens hobbyist that enjoys spending time caring for her fish and helping new betta keepers learn the ropes. More posts by:

2 Comments for this entry

  1. Anonymous says:

    My Betta likes to lay face down on rocks in bottom of tank…if i come over and move tank a bit he startles off and swims around. He is eating and looks at me when i go to feed him. Why is he always laying at bottom…it scares me!

  2. Wow! This can be one particular of the most helpful blogs We have ever arrive across on this subject. Basically Great. I am also a specialist in this topic therefore I can understand your effort.

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