Prematured molly babies

[Mollyfryfry]

Okay so my not so pregnant molly gave birth to prematured fry, I'm sure all are dead and she was still giving birth a few mins ago now she stopped.
Now there's another pregnant molly in the tank and the water is a little dirty so I just changed a bit and put little warm water, now there's prematured babies lying Everywhere, when am I supposed to clean the tank? I'm new to this molly breeding

 

[Circus]

I do a large water change after any fish death. Make sure all of the dead fry are removed from the tank. Some livebearers will abort their current batch if they are too stressed out.

What are your ph, gh, and tank size? How long has your tank been set up, and what is the stock?