All My Fish Just Died

I'm sorry to hear this.

I need to ask you a lot of questions, I'm afraid.


How long has the tank been running? If it is new, did you cycle the filter before getting any fish?
Have you bought any new fish in the last couple of weeks?
Have you sprayed anything in the same room as the tank, done any decorating, used any air fresheners, or anything like that?
How often, and how big were your water changes?
Do you know the pH of the tank water just before or after the fish had died? If you haven't emptied the tank yet, test the pH or take a sample now ready to take to a shop when they open for them to test it.
Do you know how hard your water is? Does your kettle/shower head fur up - that's hard water if they do. Or look on your water supplier's website.
Do you know your KH? KH is a type of hardness that buffers the water against pH changes. It is not the same as the hardness that furs up the kettle, but they tend to be low or high together. If you have soft water you are likely to have low KH.



If the tank was new and you didn't do a fishless cycle, they could have died from ammonia poisoning. Neons are the most susceptible of your fish, and when they died their bodies would have decomposed to make even more ammonia.

If you have bought new fish, they could have brought in a disease. There are some that could have wiped out a whole tank that fast.

If you have used air fresheners etc, they can get into the water and poison the fish.

The community creator puts you at 175% stocked (though I did have to substitute 5 smaller panda cories as peppered cories aren't in the database). This amount of fish makes a lot of waste, especially the two bristlenoses. Lots of waste means lots of ammonia which the filter turns into huge amounts of nitrate.
Around 12 years ago, I got up one morning to find every fish in the tank dead. I had no idea what happened back than as we didn't have internet access. But with hindsight, I think I know now what happened. I will explain what I suspect happened to my tank, see if it fits with yours.
I have softish water that has a low KH. My tank was overstocked so lots of nitrate, which is acidic and pushes the pH down. I didn't do big enough or often enough water changes which allowed the nitrate to build up and my low KH to get used up. I didn't have a test kit so this is my best guess - the pH dropped very low very quickly and that killed my fish.


What to do.

If the tank was new, empty the water, refill and do a fishless cycle before getting any more fish.

If it was a disease brought in by new fish, you will need to remove every trace of it before restocking the tank. Unfortunately that means sterilising the tank with bleach, then re-cycling the filter. I do know that is not a pleasant prospect; it is what I had to do when my betta got lymphocystis. It was 6 weeks before I could get another betta.

If it was something in the air, you need to empty all the water and refill the tank. The filter bacteria should be unaffected but it is worth getting a bottle of ammonia solution and adding some to check the filter can process it before getting more fish - and stop spraying, using air fresheners, whatever it was. Use the fishless cycling method for the amount of ammonia to use.

That leaves possibility number 4.
The first thing to do is test the tank water's pH to see if it has dropped very low. A shop will be able to test this if you don't have your own tester. Take a sample from the tank now ready to test when the shops open. And you need to know your KH - again a shop will test for you but for this take a sample of tap water as you need to know how much buffering capacity your tap water has. And it's KH you need to know not GH so make that clear to the shop.
If it does turn out that you have low KH in your tapwater and your tank's pH did drop very low, you can restock the tank, with precautions to avoid this happening again. First, change all the water. That will reset your KH and pH back to tapwater levels. Then you can get more fish fairly quickly before the filter bacteria go dormant though lack of food. But this time don't get as many fish! Use the community creator on this site so you know when the tank is full. Click on fish profiles in the menu at the top, click on any fish then scroll down to the bottom of the page. Just enter the tank details and add fish from the profiles. If you want to save your tank, you do have to register and log in separately from the forum.
I would not get more bristlenoses for this tank as it isn't really big enough and they do produce a huge amount of waste for their size. And if you want cories, choose 6 of one of the dwarf species. The most common one in shops is pygmy cories but that isn't in the fish profiles. Use salt & pepper cories (which aren't the same as your peppered cories) in the CC.



Sorry for the essay, but I do know what it is like to lose a whole tank of fish. See which of the possibilities is the most likely for you - and any others that other members can think of.

Can I use just standard household bleach, I have parazone citrus, or do I need to go buy something different?

They did say that the ammonia was high and that is probably what killed the fish.  I probably didn't explain too well, they did just say that they had seen higher levels in samples.

Sorry you posted at same time as me.
Looks like you have your answer and people with more experience than me will be able to help you...

I agree. The only time sterilising a tank is necessary is if the fish died of some disease. I had to sterilise my betta's tank as lymphocystis is a contagious viral disease and I couldn't risk there being any trace of it left.

Three weeks is too long for one of those diseases that spreads fast and can wipe out a tank. It would have happened within a week in this scenario. This rules out option2.

Your water type does rule out option 4, ie low KH and a pH crash.

That leaves airborne contaminant (option 3) but you haven't mentioned anything along those lines; and option 1.



I'm going to assume you don't know about cycling, please ignore all this if you do know.
Fish make ammonia as part of their waste. Ammonia burns the fish's skin and gills making it hard to breathe. In a cycled tank, a colony of bacteria livesin the filter which uses ammonia as food, and they turn it into nitrite. Nitrite is also toxic as it binds to the fish's blood so it can't carry enough oxygen. A cycled filter contains a second bacteria colony which uses nitrite as food and turns it into nitrate, which is much less toxic than the other two. In most tanks, there are no bacteria that eat nitrate, and we remove it by doing water changes.

Unless you do a fishless cycle before getting fish, when you first put fish in the tank there are no bacteria to eat the ammonia made by the fish. You have to monitor the level and do water changes to keep it low until enough bacteria have grown. Once the ammonia eaters start to grow, they make nitrite and you have to do water changes to keep that low as well. Keeping the levels low does not stop the bacteria growing; as long as there is a trace more than the current numbers can eat, they will  multiply.
There is an added problem for you. Ammonia exists in two forms, ammonia and ammonium. There is always some of both in a tank but it is the ammonia form which is the toxic one. The amount in each form is pH dependent. The higher the pH the more ammonia, so with your pH you will have a higher proportion of the toxic form than someone with low pH. It is more important for you to keep your ammonia level low.

Since you didn't have an ammonia tester, it is possible that you had quite high levels when you first got fish. This does affect the fish, even if they don't die. It shortens their lives and makes them more prone to infections. Neon tetras are fish that don't do well in tanks less than six months old. It is thought they need some micro-organisms in the water to do well, and they commonly just die for no apparent reason in tanks too young to have grown all these micro-organisms. And your hard water and high pH would have put extra stress on them as they prefer soft acidic water.
I suspect you had some ammonia in the tank to start with, then the neons died and would have made even more as they started to decompose. The fact that you did a 20% water change and still had ammonia means that it was indeed likely to have been higher before the water change.
Re your shop's comments, it is always best to get them to write down the actual readings. Them saying things like 'fine' or a 'bit high' is just their interpretation. The only 'fine' reading is zero!

You will already have some bacteria in your filter, quite possibly enough for a smaller number of fish. The simplest thing to do is get some ammonia solution. I think Homebase still sells it, in their cleaning section. Failing that, Ebay or Amazon. Read the desciption carefully as you don't want any other chemicals in there. Then follow these instructions. If you do have a lot of bacteria there, you will get zero ammonia and nitrite 24 hours after adding a dose of ammonia. This means the filter has enough bacteria for a suitable number of fish. If either/both are not zero after 24 hours, just carry on with the instructions until they are.




The cories wouldn't have been salt & pepper as they only grow to 3cm at adult size, yours were already bigger than that. I'm afraid I have no idea which species they were, google doesn't come up with any results. It could well be a common name the shop or their wholesaler made up. And salt & pepper cories (Corydoras habrosus) are not very common. I'm trying to get some but I haven't yet found a shop that has any 
Platy females usually arrive in your tank pregnant. They can store sperm, so if they've ever been in a tank with a male for longer than about 10 seconds, they will be able to have fry for about six months.

When using the Community Creator I try to substitute a similar fish, adjusting the numbers if the substitute is bigger or smaller. When I entered your fish I used the smaller panda cories but 5 of them instead of 3. Your gold zebra danios are a colour morph of regular zebra danios, so that's what should be entered in the CC.



Another long essay (sorry    ) but there is something I do need to check. Have you done anything to your filter?
A lot of manufacturer's instructions say to change the media every so-many weeks. If you do this, you throw away the majority of your bacteria. Have you been doing this? Have you washed the filter media, and if so what in? Plain tapwater contains chlorine or chloramine which is there to kill bacteria in drinking water and will also kill your filter bacteria. Media should be washed in old tank water taken out during a water change.

I have a personal preference for Eheim filters, but they are not cheap 

For 60 litres, look at Eheim Aquaball 130 (type 2104). I know the 60 model is rated for up to 60 litre tanks, but I prefer to use filters rated for slightly bigger tanks and the 130 is only a few pounds more. They do have a flow adjuster. Fluval is another good make.

Would this be a marina s (number) filter? We've recently had someone else with a Marina tank and this filter. The cartridges are either biocarb or bioclear according to the manual for their filter. The biocarb ones contain a biological medium plus carbon. Carbon gets full quickly, that's why they tell you to change those. But you don't actually need carbon, it's a hangover from decades ago. The bioclear cartridges contain a biological medium and zeolite - and zeolite's sole use is to remove ammonia. Until it gets full when it stops. Because it removes ammonia, the ammonia eating bacteria don't grow well and when the cartridge stops removing ammonia there won't be enough bacteria so ammonia builds up.
In my opinion, the best thing to do is stop using bioclear cartridges (the zeolite ones) and add sponge to the filter instead. Any make filter sponge will do, just cut it up to make it fit. Then just wash the sponge, don't change it.