Fish dying

[Kolenc]

I have many fish for months. Than all of a sudden a couple with die within a day or two. Than the rest are fine. Any ideas?

 

[ZxC]

Do you have a freshwater test kit?
Usually we need to know ammonia/nitrite/nitrate/pH/temperature values before we can help. Fish species, tank size, filtration and any other info you can provide may help. Any signs of disease?

 

[King Fisher]

I'll add fish stocking number

 

[Angellove78]

Need more info. Test levels, what kinda of fish+ how many, water changing schedule, what size tank, Filtering system, temp? Is the tank cycled? And have you added anything new to the tank?