grow-our tank now death-tank. what went wrong

[fishcakes]

Here goes.
I've had a 30g grow-out tank for some time now. Only problem before was a batch of albino zebras that just had issues, so they were removed.
I am now watching them die off one by one and fast. They tip to their sides, swim wildly in circles and gasp. They have plenty of air and water flow. Some when dead have mouths gaped wide open. I just don't get it.
Since then things were fine more batches were added. Blaa, Blaa, blaa. Well this weekend I finally got sick of fighting with the sun and moved the tank to the basement storage room. They kept a good amount of their water they always had a glass bottom so rock is not a issue I switched to a HOB filter. I one problem was heat. The room is not insulated so getting up to temp was slow. We now have it insulated and one meter is reading 77.8 and another 80. I had a oh crap moment and realized I didn't use old filter media from their old sponge filter, but yet what they had was not straight out of a box either.
So is it filter related? Heat? Light? What?

 

[Dreamingdragon]

Sounds like ammonia poisoning to me.

 

[Aski247]

Sounds like ammonia poisoning to me.

Yup. That would be my guess. Poor water quality.

 

[fishcakes]

I tested all water areas and all were fine including ammonia. I'm treating water anyways.
I just don't get what's going on.

 

[Dreamingdragon]

Or you had a ammonia pike. Because if fish starts to gasp for air it's ammonia poisoning you can see it when there gills or open when they or dead and wide open mouth. Do you use API test kit ore dip stick.

 

[fishcakes]

I use API

 

[Dreamingdragon]

So how is it going so far. Is your tank stable

 

[fishcakes]

There have now been no deaths for a few days now. I came to the conclusion that before I moved it down to the basement I cleaned it too well. I was so sick of the brown from the sun that I went overboard, and well the tank was like new and had to cycle again.
Live and Learn.