This is the post I never wanted to make so please if anyone needs to criticise do it gently. I'm beating myself up about this enough as it is, don't need anyone else to do it for me.

I've just killed my fish...

Over the last couple of months I set up my tank, as mentioned on the other threads I started. It's a 110 litre, with an internal power filter, heater etc.

Everything was fine and I added my first two fish - two small bistlenose plecs. Checked the water every day, saw the ammonia spike then drop, the nitrite spike then drop, etc as predicted. When it settled I added a siamese fighter. Same again, everything fine. A couple of weeks later I added 11 cardinal tetra. Everything was going fine - the filter seemed to be coping fine, water was testing fine for everything, the temperature had balanced out to around 25. I've been doing partial water changes (about 5-15 %) 2 or 3 times a week.

Then I went away for a week. Everything I read, various fishkeepers I've spoken to, and the people in the fish shop, all said the same thing - fish will do fine without food for up to a couple of weeks. The way I understood it using a feeder block or getting someone to feed them is risky in case of overfeeding and messing up the water quality.

So I did a couple of extra water changes before I went to get the nitrate levels right down, made sure everything was working, fed them immediately before I left and thought they would be ok.

Came home last night to a massacre - the bristlenose and tetra all dead, and for some time judging by the state of them (colourless, half disintegrating).

Dali (the fighter) was the only one still alive - when I first saw him I thought he was dead too (motionless at the top) then he started moving. He looks like he's been nipped a fair bit, but over the course of the alast 12 hours has perked up a bit and is at least acting fairly normally.

Obviously the first thing I did was check evrything - heater and filter still appear to be working, the temp is still reading at 25, and the water tested clear of both ammonia and nitrite (and chlorine obviously). Even nitrate levels were still low.
I did a 10% change there and then and removed all the bodies, and I've done another 15% or so today. I've fed Dali a few times and he is eating fine and definitly looks better (no visible issues, other then nipped fins).

I'm just devastated. They had all been together about 3 weeks with no signs of anything being wrong and now this. I feel so guilty like I've murdered them all but I don't get why it happened.

If anyone has any ideas or advice that would be fab - I don't want to lose Dali too! I'm also really scared about getting any more fish in case it happens again. (Not that I would do so anyway until I'm certain everything is fine, but for future reference). Could it be that one was sick anyway or did I starve the poor things to death?

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"For all its sham, drudgery and broken dreams it is still a beautiful world"

I'm so sorry for your loss!! It's an awful thing to return home to. I know how you feel. I had a tank of cold water fish and one day my niece was over and she asked if she could feed them. I had already taught how much to put in and everything and I was distracted in the bathroom giving my Yorkie a bath and said that she could. She had been snacking on some dry crunchy nut cornflakes and she fed them those instead of fish food. I didn't know she had. The fish started dying one by one and I couldn't understand it. I had two shubunkins left (sun and jin) and took them out and put them into a different tank overnight as I guessed it was something in the water (infection or whatever) but they died too. Then she told me what she had done. So it turns out that fish have a nut allergy

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Bonnie 29.01.97 - 21.09.11
Millie 01.02.01
Seamus 09.07.00
Tyler 08.11.00
Kiki 15.10.10
Chico 01.07.11
Riley & Louie 16.02.11
Holly & Ivy - 11.11.11

If they had starved i would expect one at a time to die and as they did be eaten by the others

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Don't like asking this but could anyone have gotten into your property and did something to them? Either accidently or purposely?

Yes it does sound strange. I've left my fish for two weeks before with just a feeding block and they did fine.

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Bonnie 29.01.97 - 21.09.11
Millie 01.02.01
Seamus 09.07.00
Tyler 08.11.00
Kiki 15.10.10
Chico 01.07.11
Riley & Louie 16.02.11
Holly & Ivy - 11.11.11

Thanks folks. I don't think anyone has been in - nobody has keys that I know of (we had both sets with us) and I can't see my ex making a copy of them just to break in and kill my fish.

Its just odd and very very sad. Didn't realise I could get so attached to them. Fingers crossed Dali makes it now.

Welshyorkielover - that's awful :-(

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"For all its sham, drudgery and broken dreams it is still a beautiful world"

How awful for you to come home to that. I keep tropical fish, and you do get attached to them.

I have also heard that you can leave the tank for a couple of weeks, although I haven't been in a position to test tht theory. The longest I have been away is 10days, and I got a bit nervous about leaving them with no food, so bought the tetra holiday food block. It is not one of those white blocks - I have heard they really mess up the water - but rather, a kind of compacted jellified disk of food/nutrients which disolves slowly as the fish nibble at it. So far that has worked fine for my tank. I may lose maybe one fish while I am away, but I think it is more a coincidence rather than because I am away.

I have never kept a Siamese fighter, but wonder if maybe the fact that it is the only survivor,that perhaps it somehow set upon the other fish. I would have to do a bit of research on them. I know males will fight each other, hence only having one in the tank, but don't know if they would attack other breeds of fish.

Could you have had a powercut while you were away - may have caused a drop in temp, or toxins to build up temporarily. Just a thought.

Just done a quick bit of researching on-line, and there are definitely reports of some male fighters attacking other fish, especially colourful ones, mistaking them for other male fighters. Not every male will do this. They have different temperaments, just like people, so some are placid and some are more aggressive. Of course, I can't be certain this is what happened in your tank though.

How long had you had the siamese fighter before you went away?

It is possible your betta went hungry and started attacking although I would think the tetras were too fast for him

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Doglets: Teal, Dylan and Buster

Ponies: Toffee, Samba and Jake

Guinea wiggles: Hector, Herbert and Humphrey

Fishes: Bess, Gerald, Barney and Claus

Unusual. At first I thought maybe something crashed but had corrected itself by the time you got back (electrical failure cutting out the filter) but you would expect to see a higher level of nitrate if that was the case. It won't be food so don't feel guilty about that- I have left fish for longer than that without any problems.

It is interesting that your survivor is a fish that can breathe o2 from the air.

Whatever it is - it has been environmental, it almost always is when you get a sudden mass death of everything. It has the hallmarks of poisoning but it is hard to see how when nothing has got to the tank? All very weird.