In this forum, you will see a sticky called "FishLore Articles for Beginners". Please read these articles. They will give you a lot of insight into what is happening with your tank. You need to fully understand the cycling process to have a healthy tank. Please ask any questions you run into. If you don't get the cycling process, your fish will probably stay sick or die, and you will not stay in the hobby very long. We want you to stay, and we want your fish to stay healthy!
First off, your tank is way too small for 2 mollys. A 5 gallon tank is very limited by what can survive happily in that size tank. You need at least a 10 gallon tank for those 2 fish, but first, your tank needs to be cycled. Because of the size of your tank, your mollys are putting out a lot of
ammonia when they poop, pee, and breathe. You don't have the right bacteria right now to eat the ammonia your fish are putting out, and the level rises. A tank usually takes at least a month to cycle, and it's recommended that you cycle a tank without fish because it is very stressful for them, and could also kill them. I answered your other post based on the information you provided, and now that I have more information, you will probably have to be doing daily water changes. The cycle product is not very popular with hobbyists, and I have read that it will also raise the nitrate level in the tank. I would suggest that you quit using that product for now because I don't think it is helping your tank right now. I would also suggest you get your own testing supplies. If you click on the PetSmart website, search for an Aquarium Pharmaceuticals Master
test kit for freshwater. They are under $15.00, and if you copy the page that shows the kit and the price, your local PetSmart store should honor the online price. Tanks always have a knack of having problems when your local store is closed like at midnight, and you will really enjoy the convenience of having your own kit at home.