Fish dying without reason 75 gallon tank

[ttmoreno]

Have a new tank that has been set up for a year. Cannot keep fish alive for more than a day.
Water tests fine with API Water testing kit, strips, and at three different fish stores in my area. Even went to one that was almost 50 miles away and they could not help me.
I have even tried the little feeder fish to see if they would live in the tank.
I have well water and had it tested and it tests fine as well.
I acclimate the fish like I have been told.
Nothing new in tank.
I have two filters/ two heaters, aerator, 3 decorations, black gravel.
I don't know what else to do. Using wall chemicals i have been told to use to pre treat the water.
I was really hoping someone on here would have had same problem and tell me what to do>please help I want to have fish!

 

[Magaratz]

Give us a little more on how they die—gasping at surface, trouble swimming, body shows lesions, anything out of the ordinary? My gut tells me there’s something in the well water that’s not being discovered. I’m not an expert on what well water can have that’s a negative.

 

[Aiken Drum]

You've never had a fish survive more than a day? You have been trying for a year? Thats dedication and perseverance right there.

What fish have you tried with?

Have any of your tests been for water hardness? Maybe there is a big difference between your well water and what the fish stores use.

Sorry if im dumb, but i presume well water isnt chlorinated? Could there be something else in there that a home aquarium test isnt picking up? Have you had a professional carry out tests similar to what our water supplier does monthly? A full breakdown of everything in the water in much more detail than a home test kit can provide.

Have you ever tried filtered water? Or bottled water?

What exactly is your acclimatising method?

What water conditioners have you used?

Any physical signs of what the fish are going through before they die? Gasping at the surface? Redness around gills? Any clues?

 

[ttmoreno]

I have tried all freshwater fish. We had a tank before and never had a problem this is a brand new tank we bought at PetSmart. The only difference is the lights. We have had our well water tested as well as our aquarium water.
Never tried filtered or bottled water.
Acclimating fish by adding small amounts to bag from aquarium water over a 30 minute period.
API stress coat

 

[ttmoreno]

Oh forgot that there is no sign of problems with the fish. We have bought from several different fish stores. They all die overnight. They are fine swimming around and then wake up and they are dead.

 

[Aiken Drum]

Maybe consider getting an RO/DI filter, start from scratch with pure water and remineralise. Unless there is something so obvious to us we dont think to mention it, but is just totally off your radar.

Water temperature maybe?

Or perhaps something so far out there nobody considers it.

An electrical fault with some equipment in the water?

Some trial and error might be needed.

Empty the tank, go bare bottom. No decorations or anything. See if that makes a difference.

Try a different tank. If you keep a fish in there ok with your well water its probably something to do with your tank or contents.