Established tank all fish died

[Jbsteel87]

I think from whats been said I'd agree with people that it looks like ammonia poisoning over the course of a few days. Even at low levels .5 or .25 it can kill fish. Really sorry to hear you had some of these for a long time too.

I had a really big disease outbreak in one of my tanks quite a few years ago and lost a lot of fish really quickly and it is a punch to the gut when it happens infront of you.

Like above I'd recommend getting an API liquid test kit they are the ones most people go by so have a level of trust that is worth paying attention to.

I am curious as to what could have caused the ammonia in the tank though, I think if we get to the bottom of that you will have more success in the future. So if you don't mind a few more questions

How often to do you clean your filter? And is it internal or external?

Do you have a gravel substrate and how deep is it and how much do you clean it? A

re any of your plants doing badly and do you know if you have any terrestrial plants in there?

When you feed them is there ever food left over and if so do you remove it or leave it in there?

You mentioned about some difficult times when tank maintenance drops off (it happens to us all, pretty unrealistic to think otherwise) but when things are more settled what is your maintenance routine? Do you do weekly water changes etc? And when you do a water change how much do you each time?

Last thing to mention - might be worth just putting some food in the tank to rot now and feed the filter until new livestock is added.

Wills

This aquarium has a three chambers in the back. Water fills the first overflows into the second, runs though the filters,then is pumped back into the tank. I Clean main filters every 3-4 weeks. There is a nitrite, black carbon sponge and floss filter. 2. 5 inches of gravel substrate. It gets cleaned every 4 weeks unless I see it is very dirty. There is usually not food left over. The one plant looks rough others are good. I usually don't do weekly changes. When I do it's usually 40%

 

[CaptainBarnicles]

Weekly water changes will keep your tank healthy, fresh water is key...

A little illustration for you...if you were to spill bleach or something corrosive on your skin by accident, would you pour another chemical over the top to 'neutralise' it or would you just shove it under a running tap? Anytime you find ammonia in your tank, fresh, clean water

 

[itiwhetu]

How much of your tank has live plants. Like is it a third or half.

 

[itiwhetu]

Do you know what your pH was before this happened.