Your Molly
Hello Mik...
Livebearer females can hold their young until they feel water conditions are just right to ensure the survival of the fry. Mollies are the most particular about stable water conditions than the other Livebearers like Platys, Guppies, Swordtails, etc.
Large, frequent water changes are the only way to ensure the water properties are always stable. If your Molly is close to giving birth, then a large water change with treated tap water that's a bit warmer than usual will help.
If you're not adding a teaspoon of standard aquarium salt to your replacement water, you should consider it. Livebearing fish are typically raised in areas of the country that contain a bit of salt in the water.
I've kept Livebearers for about 8 years and have always included a teaspoon of standard aquarium salt, or Kosher salt or canning salt to every 5 gallons of new, treated tap water.
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