hi and welcome,
can you post a picture of the molly?
What are you worried about with your tank? Is it big enough? Let us know the dimensions and stocking of fish etc.
What are your water conditions (ammonia, nitrite, nitrate) and parameters (temperature, pH, GH, KH)? If you don't have the test kits you can ask your local fish shop to test the water for you. Your water suppliers website should publish the pH and GH - if you can't find what we need, post a link so we can have a look.
In the meantime clean the gravel and change 75% of the water for fresh dechlorinated water.