Huge Spike In Ammonia, Nitrite And Nitrate!!!!!

When did you last test the water before yesterday? 8 ppm is a huge amount of ammonia, and if the tester is like mine and only goes up to 8, it could have been higher. A tank full of fish will make less than 3 ppm in 24 hours. And it is too quick for dead fish to make that amount.

I'm not sure the sand is to blame if it has been in there 5 weeks. What brand was it?

How deep is the sand? Gas pockets usually form only in deep sand.
Would you consider getting Malaysian trumpet snails, they live in the substrate during the day and aerate it well.

Did you touch the filter during the water change?

Have you added any new fish since you redid the tank?

Silly question but are you absolutely sure it was dechlorinator you used not another bottle in the cupboard?

Do you use air fresheners, or did anyone use an aerosol in the room yesterday?

One other thing that does occur to me and that is to contact the water company to see if they did something to the water supply yesterday. I was once told by a shop that a lot of his customers had fish die when they did a water change on a Saturday. One customer contacted the water company and was told it was because they flush lime through the system on Saturdays. (Though why they'd want to flush lime I don't know, though it could have been something to remove lime, it was a third hand comment). I've also read that in the USA they use extra chlorine/chloramine after heavy rain. So water companies do sometimes do things to the water which can affect fish.



You could try washing the sand. As it has been in there only 5 weeks it won't have much biofilm and bacteria on it yet. I would also do a water change to get the ammonia level down to 3 or 4 ppm. Then I would leave it fishless and monitor the water. That will tell you if it is a problem with the filter. Since you have live plants, they will help too.

I do understand what it is like. I have twice got up to find a tank full of dead fish (about 16 and 14 years ago). I think that not knowing what happened makes things worse. I restocked on both occasions. The first time the fish were healthy for a couple of years and it never happened again after the second time.

Very sorry to read of this; if I were you, I'd have to get to the bottom of the ammonia spike, so definitely contact the water company as Sue suggests.

Other thoughts - which I'm sure you've already considered - are:
* change in feeding habits - have you been feeding more lately, and have you watched to ensure the fish have been eating the food (eg it's possible that the stress of the change of tank decor may have reduced their appetites and that the food has gone uneaten and decomposed)
* did any fish go missing recently and which may have decomposed into the gravel which then got disturbed during the substrate change and still be in there?
* is the filter functioning properly or is the flow weaker and it clogged up or the impellor stuck?
* what is the live bacteria which you mentioned dosing the tank with?
* the water conditioner - is it definitely a dechlorinator?

It's just struck me that I have some Seachem AmGuard from my goldfish-keeping days which I'd completely forgotten about. I'm wondering if that would be of help to you? @Sue might know better. [I'm guessing that, having not been touched for 3+ years, and possibly as long ago as 6 years, it probably wouldn't be of any use for me to send you some of it in the mail and that I should maybe just bin it? Thoughts welcome.]

Still playing on my mind as to what could have caused your ammonia spike. Is there any possibility that someone could have spilled anything into the tank, such as a guest setting down a glass of alcohol during a party, a mischievous or well-meaning child, or anyone being over-exuberant with cleaning the house?

[As I write this, I've suddenly recalled that my goldfish used to freak out on the rare occasion that we used to burn a candle - I always assumed that the flicker of the flame disconcerted him but now I wonder if it was the scent from the candle that perturbed him and whether that might have upset the water quality. We don't tend to burn candles anymore - and I realise it would probably be unwise to burn the scented ones with fish around.]