Water testing at pet stores are not the best choice. Many of them always say it is perfect when it is not. You need to get the actual readings instead of the word "perfect" from them.  Better yet, get your own test kit. API Freshwater Master kit is cheap, and you can do 100~150 tests with it at home, no need to go out and get your water tested. Totally worth the investment.
Weekly partial water change is recommended instead of once every two weeks. You've also been feeding too much. Molly can't eat two corn sized pellets per day. Those two pellets are more than enough for a dozen Mollies.
I am also interested in how you cleaned your tank 7 days ago.
Often when people are not careful when they clean the tank, they might crash the nitrogen cycle or partially crash it into a mini-cycle. When I clean my fish tanks, I do not go beyond clean the side of tanks with algae scraper or 100% cotton clothes, plus vacuum the substrate. Did you clean the filter? If so, how did you do it? That part had to be done extremely careful under old tank water or (treated) tap water, or the beneficial bacteria could be killed by chlorine. The filter media also must stay wet the whole time.
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