MILKY WATER & SOME FISH HAS DIED

[Marc West]

Changing the substrate has messed up the cycle which is why you have ammonia and fish at the surface.
Do you have another tank which is cycled? You could then move some filter media and substrate from the cycled tank.
Do you have any bottled bacteria to add?
Do you still have the old substrate?
You will need to keep doing water changes whenever ammonia or nitrite go above zero.

Changing the substrate has messed up the cycle which is why you have ammonia and fish at the surface.
Do you have another tank which is cycled? You could then move some filter media and substrate from the cycled tank.
Do you have any bottled bacteria to add?
Do you still have the old substrate?
You will need to keep doing water changes whenever ammonia or nitrite go above zero.

Only other tank is the 5ft Fahaka tank. The media in the filters are mature. I have loads of liquid stuff, from api quick start, water conditioner, ammonia&niritie remover, stress coat. I'll keep doing big water changes.
Having got any old substrate left