Sudden Bacterial Bloom on Established Tank + Fish Deaths - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 6 Old 11-17-2008, 06:41 PM Thread Starter
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Sudden Bacterial Bloom on Established Tank + Fish Deaths

My 20g tank went from perfectly smooth to disaster in the space of a couple of hours while I wasn't around. The tank contained 6 tiger barbs, 1 dwarf puffer and 1 clown pleco. So far, one barb (the dominant male) and the puffer have died. The water went from crystal clear to a watered-down milk color within the space of hours, which screams bacterial bloom to me. Tank maintenance is always done regularly so I don't always do regular testing, but of course I tested the tank right away. No ammonia, no nitrite, 10 ppm nitrate but I did a 50% water change just to be sure. Post-change there was no ammonia, no nitrite and 5 ppm nitrate. The fish were gasping at the surface. The tiger barb died this morning, and the puffer died about an hour ago. I just did another 50% water change but the water is still cloudy.

What could be the reason for this bacterial bloom? The parameters are all in check. The only thing unusual I noticed is that the driftwood started to grow some weird white slimy mold stuff, which spread to the filter intake right before the bacterial bloom. Could this be related?

So, my questions are: can I assume that if my water parameters all checked out that the fish died due to oxygen depletion because of the bacterial bloom? Also, what could be the cause of the bloom? These fish haven't been overfed and like I said, I'm pretty anal about tank maintenance and water changes. Is there anything I can do to halt it? The water change last night cleared the water up a bit but it was cloudy again today, so these bacteria are still multiplying. I did a bit of research but all I could find on bacterial blooms was related to new tanks and escalated ammonia levels.

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post #2 of 6 Old 11-17-2008, 07:04 PM
I have no clue why this could have happened. You could try adding a medication that takes care of gram negative and positive bacteria (because there's really no way for you to tell without the proper equipment) to get rid of it. You could also try salt, but it may not work well enough for such a severe infestation. I am guessing that it will not go away quickly on its own if water quality was not an issue and it is continuing to multiply.

Were there any airborne contaminants lately? How long ago did you get the driftwood and where did it come from?
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post #3 of 6 Old 11-17-2008, 07:13 PM
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That's strange for sure, cause it's obvious that you take well care of your fishies. Do you have anywhere else to put your other fish just in case until it gets cleared up? I would imagine it's definitely cause of the driftwood... that worry of it eventually rotting has been kinda been lingering in my mind.

Also, this brings back an amusing memory for me that I will share. Lol, a few years ago or so, I had about 5 feeder goldfish, just little ones, in a 10 gallon. Well, I'm artistic and this particular thing I was doing, I was burning the edges of the poster board I was working on. One corner of it got outta control and I panicked... so I'm in my bedroom right, waving this flaming smoking piece of art around my head to try and put it out, cause blowing on it wasn't helping, lol. Not wanting to burn the whole apartment building down, I quickly noticed my fish tank which didn't have a cover and I dunked it in there. Now I can't remember how long after that my fish died, but the tank had quite a smoky look for a while. I wasn't as knowledgeable then as I have grown to be in the last month or so. So ... never light fires that you can't control mmkay? :)

Last edited by SolaceTiger; 11-17-2008 at 07:19 PM. Reason: Had to tell a funny story. :x
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post #4 of 6 Old 11-18-2008, 10:09 AM Thread Starter
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The driftwood with the fuzzy stuff had been in the tank for almost a year. Another piece (non-fuzzy) had been in the tank for about three months. Last night's water change helped clear it up some, but to my surprise the water was almost completely clear this morning. No more deaths, and the remaining fish seem just fine. I guess the problem's over, but I'm still really curious about what caused the bloom in the first place so I can prevent it from ever happening again.

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post #5 of 6 Old 11-18-2008, 11:40 AM
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Anyone else have access to the tank? did you service the filter recently? I have heard of sudden ammonia spikes that were unexplainable and dissapeared just as quickly as they appeared.

The most important medication in your fish medicine cabinet is.. Clean water.
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post #6 of 6 Old 11-18-2008, 12:15 PM Thread Starter
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My girlfriend also has access to the tank, but she knows her aquarium care so I don't think she would have messed with it. The tank has an undergravel filter (air pump driven) as well as a Tetra HOB. The Tetra stopped running...two weeks ago?...and was non-functioning for several hours before I noticed and got it running again. It was full of water the whole time so the filter media stayed wet.

The only thing I can think of is that whatever mold or fungus (it didn't seem like algae at all) was growing on that log had a sudden die-off that spiked the ammonia temporarily. That, or maybe the UGF was disturbed somehow.

Now we have to look at putting some more stock in the tank. We'll wait a week or so just to be on the safe side before adding any fish, of course. I think we'll add a green tiger barb or two since the school of regular tigers is down to five. There's still the clown pleco in the tank. We might try puffers again, but honestly I'm a little scared that we may have just lucked out and had really docile puffers last time so it might be a risk. Anyone have any other suggestions?

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