First, hi Jetosy and welcome to the forum.
This section is mainly for people to introduce themselves when they join. Unfortunately, not a lot of members come here to welcome them. This question probably should be in the Beginners section. When you're new, its hard to figure out what goes where. It's not a big problem, you just won't get many replies here.
As for the question, you are right that generally if a fish is spending a lot of time at the top almost like their grazing the top or feeding, it usually means they need oxygen. What temperature do you have the heater set on? High temperatures can drive oxygen from the water. I know that some medications tell you to turn the temperature up but don't know if that is the case with what you used or not. It doesn't look like there's any problem with your water parameters.
PM one of the moderators (names in blue at the bottom of the Forum Index page) and have them move this to the beginners section or maybe even the livebearers section. I don't have any mollys so I'm not really very knowledgable on them. That may be normal behavior for them. I think they generally do prefer the top portion of the tank anyway.