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Fish catastrophe

mjbarnard

Member
Joined
12 May 2010
Messages
48
Location
West London
This is a very strange problem. I woke up this morning to find 5 dead fish and the rest gasping at the top for air. I have solved it with some immediate water changes, but do not understand it.

3 year old established tank - 125 litres. Always been overfiltered - Eheim Pro 3 2073, suitable for aquariums up to 350L. Media and filter absolutely established and water parameters have always been fine, no ammonia or nitrite ever. This is such a well established tank and filter that I couldnt believe this was a water quality issue.

25-30% water change weekly and monthly filter maintenance.

16 Rainbowfish which is well stocked, but the filtration and long term stability mean they have been absolutely fine. Up until last night they all looked healthy and active. One of the deaths was a mature blue rainbowfish who has been present in the tank from the very beginning, and always appeared healthy and active, whatever was going on.

Yesterday I did two things :
1) I did an approximate 40% water change.
2) Just before going to bed, I fed them some defrosted frozen food. Gamma blister brineshimp + spirulina. The food was from two packets, both of which were half empty, having been fed to them before. The only difference was that usually I sieve the defrosted food before feeding, but for some reason I didnt. I feed dry flake food during the week, and frozen food every Sunday.

I have recently installed a new 500L planted tank next to this one, so I have a very convenient water change system. The water empties by turning a tap from the filter outlet, where it goes directly to a drain, and there is an HMA filter plumbed in, which directly feeds the tank at the flick of a switch.

When I discovered the problem this morning I immediately took a couple of water samples and then did a 70% water change. Ammonia - 0 and Nitrites - 0. The (API) test kit must be working because ironically I did a test yesterday of the new larger tank, as I was considering moving the fish and the filter to the new tank. However there was a small amount of ammonia in the new tank (not sure why - assumed it was from plant material).

So what could have caused this?
1) Problem with the water change yesterday? Seems unlikely since changing the water this morning immediately perked all the remaining fish up, and they have appeared normal ever since. I have done a further small change this evening and they all appear fine.

2) Problem with water parameters? The tests suggest this is not the case, and the parameters have been absolutely stable for the last 3 years. No change when new fish introduced, filter maintenance etc. The tests are probably reliable, as I coincidentally checked my new tank yesterday. Unlikely due to nitrate etc, as did water change yesterday.

3) Some other disease, or toxin? No new inhabitants for several months. The only other thing I added yesterday was the frozen food. Could this be responsible?

All the fish appear much better after the water change, so I think the water and the HMA filter are good. Any thoughts? I would be interested as this is quite upsetting, and I am anxious not to allow further harm.

Thanks
Matthew
 
Very sorry to hear of your losses Matthew. Just wondering if there any other information that you could give about other components of your system/routine? It sounds as if it may be poisoning of some kind. Do you use co2?
 
Hi all,
Sorry about the fish, it is a horrible thing to wake up to. I'd suspect this is a water quality issue related to O2 content, if you are using tap water? I don't think that all the fish would have been at the water surface otherwise. My suspicion would be that
I did an approximate 40% water change
is relevant to this. We've had a lot of these sorts of reports on some of the other forums, and we think it is to do with the addition of "emergency" chloramine to the water supply by the water company where the integrity of the water main has been compromised by a leak, water metering work, etc. and there is a possibility that organic matter may have entered the drinking water supply.

At night when the bioload is all respiring and photosynthesis is not occurring, the addition of NH3 (from the break down of the chloramine) can lead to low O2 levels, even in an over-filtered, planted tank. The initial pulse of ammonia will have gone by the time of testing, and even the nitrate resulting from increased NH3 - NO2 - NO3 conversion may have already been taken up by the plants.

cheers Darrel
 
Thanks all for the interest and sympathy.

Sorry didnt make it clear. This is an established tank, which is next to a new larger tank. The new tank is now planted thanks to greenmachine, and is doing well with pressurised CO2, mod to high lighting and EI ferts. However I am establishing the new planted tank prior to transferring the fish from the old tank, and using the opportunity to stabilise the plants and adjust CO2 levels. The old tank is not planted (well it contains a couple of small plants, but is essentially unplanted - no CO2, T8 lights and no ferts).

I too was suspicious of pollutants, but couldnt think of anything likely. No sprays used nearby.

Thanks Darrel for your comments. I agree - and was very suspicious that this occurred after a water change. The symptoms looked exactly like oxygen deficiency. However I use an HMA filter from Mark Evenden of Devotedly Discus, and this removes heavy metals, chlorine and chloramine. It is only a couple of months old, and should be fully functional. The other inconsistent factor is that the remaining fish recovered promptly (within minutes) of a further large water change using the same water and the same HMA filter. They continue to appear well.

The water change was done in the morning, and the fish appeared fine all day. The feeding was done very late around midnight, with the fish appearing terrible the next morning. Is this consistent with contaminated or poisoned water?

I am suspicious of the frozen food, because when doing the emergency water change noticed that there was some still present, which has never happened before.

Thanks again
matthew
 
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