all was good except the Ammonia level was through the roof. The tube should have stayed yellow, but it turned dark green. He said that's probably what killed them, and it was amazing that the pl*co was still alive.
There is no probably about it, the ammonia definitely killed your fish.
This is what we have been trying to tell you all along.
![Wink :wink:](./images/smilies/icon/wink.gif)
Perhaps I should have been more specific.
He said the water around here has a lot of ammonia and chlorine, unless you use bottled water, also that I had overfed the pl*co
Ammonia can be present in tapwater in very small quantities, but the ammonia that killed your fish
came from the fish themselves, and all the food that went into the tank.
Ammonia is a by-product of the body when we eat food. Humans get rid of ammonia though their urine, fish excrete ammonia through their gills. Any traces of uneaten food also turn into ammonia very quickly.
Also, is the bacteria in the sponge filter any good since it was trying to survive all the ammonia?
The bacteria in the filter eat the ammonia! In a tank that is functioning properly, the ammonia gets consumed by the bacteria in the filter the moment it is excreted by the fish.
Unfortunately your tank and filter are too small, and they will never be able to support the numbers of bacteria that are required to clean the water for your fish, especially goldfish as they are messy eaters and produce huge amounts of ammonia. You should have a filter that is 2 gallons, rather than a tank!
When we talk about "cycling", this is the term for when the bacteria are building up in the tank.
This should be done with no fish in the tank.
As you have noticed, ammonia kills fish. A tank should be left for at least a month to mature before any fish are added.
I don't want to labor the point, but the tank you have is
not suitable for keeping fish.
The kindest thing to do with the last fish is take it back to the store before it dies.
I would then save up for a suitable tank and test kits.
I hope this hasn't sounded too harsh, but I think you will have much happier fish with a proper set-up.
![Very Happy :D](./images/smilies/icon/biggrin.gif)