How did you cycle your tank?
The absolutely worst way possible.
My fish store had a big sale on fish and I setup my aquarium the same day as I got a ton of fish and ended up killing like 90% of my fish.
I had a filter from another established tank and thought it would be enough but it was not.
I have a this so I can monitor the ammonia in real time 24/7
Amazon.com : Seachem Ammonia Alert : Aquarium Test Kits : Pet Supplies
This is how I first discovered that when you have Chloramines in your tap water and use tap water conditioner, the ammonia level will spike like crazy. That is why its vital you get a tap water conditioner that will detoxifie ammonia was well especially if you do big water changes.
Chloramines is a combination of both Ammonia and Chlorine. So when you use tap water conditioner it will neutralize the chlorine but leave behind the ammonia.
If you look up your water report for your tap water, you should be able to see if it has Chloramines in it.
I know that the beneficial bacteria will attack the ammonia and by using the seachem alert, I can see it slowly going down. This means the bacteria is working.
I think if you to feed them again, just do another massive water change using tap water conditioner.
I think it will work in theory but I have not actually tried it myself.
You will need.
1. Verify your tap water has Chloramines.
2. Get a Seachem Ammonia Alert so you can monitoring what is happening in real time.
3. Tap water conditioner like PRIME.
If all goes well, the ammonia will spike after each water change with you use tap water conditioner and tap water with chloramines.