My goldfish died

It was all going well untill I woke up today morning, one of my goldfish had red spots over the fins and gills, another one had a little red spot on the fin. I thought it could be ammonia poisoning (but I had changed the water just two days back) and changed 50% of the water and added 5ml of rid all general aid. I was researching about it and found it might be helpful to feed fish with live food. I took two red ants( who were already dead and floating in a bucket) washed them with fresh water and fed one to each. They chewed it for some time, than spit it, than again chewed it and finished it. After an hour or so one of my goldfish was lying at the bottom with mouth open and rarely breathing. I instantly added salt and 15ml rid all general aid to the tank. It was rarely moving fins, after half an hour, it died. The other goldfish (that had just one red spot) is still swimming actively. Did this happen because I fed ant to the fish? I feel so guilty for killing my goldfish and don't know what to do. My tank is 120 litres and had 2 goldfish in it (now just one). Please let me know what could be the reason?

 

Is this tank cycled? And what are the water parameters. Never feed your fish insects you found outside especially a type like a red ant that has venom

 

The red ants might be why. Red ants are generally toxic, they bite humans and give them a form of hives, it sounds alot like the red ants have had a similar effect on your fish.

 

Is this tank cycled? And what are the water parameters. Never feed your fish insects you found outside especially a type like a red ant that has venom

I cycled it for two weeks.

The red ants might be why. Red ants are generally toxic, they bite humans and give them a form of hives, it sounds alot like the red ants have had a similar effect on your fish.

Omg! I am so dumb

 

I cycled it for two weeks.

A fishless cycle takes average 4 to 6 weeks and a fish in cycle add on 4 to 5 weeks on top of that

You have not fully cycled in 2 weeks sadly

 

The red ants might be why. Red ants are generally toxic, they bite humans and give them a form of hives, it sounds alot like the red ants have had a similar effect on your fish.

But why nothing happened to the another one? I wonder

 

But why nothing happened to the another one? I wonder

The one that does may have been bitten before it finished eating the ant

 

Don't beat yourself up, Just take the knowledge you have gained and remember, don't feed your fish random bugs, they could be venomous even after death, carrying disease, pesticides or other contaminants.
Make sure that the tank is fully cycled before adding fish, with zero ammonia, zero nitrite But not zero nitrate.

Aquarium Nitrogen Cycle

 

Don't beat yourself up, Just take the knowledge you have gained and remember, don't feed your fish random bugs, they could be venomous even after death, carrying disease, pesticides or other contaminants.
Make sure that the tank is fully cycled before adding fish, with zero ammonia, zero nitrite But not zero nitrate.

Aquarium Nitrogen Cycle

Thanks! I will keep this in mind.