# IMPORTANT lesson about mysterious fish deaths -- have never read this anywhere



## nature (Jun 8, 2016)

SUCCINCTLY, the lesson is:

If fish are dying but parameters seem fine, *RUN WATER TESTS WITH SAMPLES FROM THE PARTS OF THE TANK FARTHEST FROM YOUR FILTER.* (I used a dropper to suck up the water from a specific spot.)

HERE IS THE LONG STORY:

After over six months of successfully keeping my ember tetras, in tanks of two sizes, I recently had a wave of deaths ... not all of them, but at least six on two different occasions, in my 29 gallon tank. After the first wave I did a major water change, which seemed to stop the deaths for about a week.

Ammonia and Nitrite were zero when I tested and I have been using Algone for nitrate so was pretty sure that was not the issue (API nitrate tests have been sold out!)

After the second wave of deaths I realised that my Kubotai Rasboras, which stay in the top four inches of the tank, and which are supposed to be very susceptible to water quality, were not affected. I did not however notice any odd symptoms in the tetras except right before they died, so I was really mystified as one of my fish died from a disease a while back and it was obvious and took a while.

A few days before the problem I had added my most mild-mannered betta to the tank (he's been great! No problems with either fish or shrimp). I have always had two filters going in the tank, one a large sponge filter, the other an internal filter which gave good water circulation. I took the internal filter out and replaced with a HOB filter (but used the sponge from the internal) because I know from experience that the Betta's tail can get stuck on the intake of the internal.

During the second wave of deaths, I thought about the rasboras being okay, and realised that the water flow had been diminished because of the changes I made to the filters to protect the betta. For aesthetic reasons both filters are in one corner of the tank. I decided to test at the very bottom corner diagonally farthest from the filters. When I did I discovered that ammonia was still zero but nitrite was quite high. It actually makes sense that if your filtration is inadequate you may have different values throughout a tank. However I have never read about this anywhere.

Thankfully once I realised this I looked more closely and found a few of the tetras did look a little off. I took them out immediately and put them into fresh water. It took a while but all three recovered and could be returned to the tank. Unfortunately between the two waves I did lose about seven tetras -- almost half of my total.

To fix the problem I made an adjustment to the HOB to increase the flow a bit. I also put a third, small sponge filter in the corner where the reading was bad. No problems since then.


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## vraev (Mar 29, 2012)

Thanks for sharing. I just got a poppy style lily pipe and noticed my fish breathing a bit more heavily at the back corner and was just wondering if this sort of scenario is possible. I have an Eheim skimmer which I’ll position at the opposite side to flow water to that spot tomorrow.


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## Fishfur (Mar 4, 2012)

I would think this kind of issue might be preventable just by adding some circulation to the tank, by way of a separate pump.

Granted, a Betta won't appreciate too much current, but a very small pump that's not very powerful, and properly placed to address such areas, would still push water around and help to alleviate this kind of thing.


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## flyingmomo (Jul 6, 2017)

I noticed that the fishes were doing very well when I was running 2 HOBs on my 20G long. Like you said, betta fins and shrimps can get stuck in intake but a prefilter sponge has been amazing. If you have one filter, adding a air pump on the opposite side has been pretty good for overall circulation.


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