New fish owner, as of the time of posting only 13 days in.

One of my mollies started having a droopy tail 3 days ago. I've been trying to read up on it, and I'm not reading good things.

The first day she acted normal up until last night she started hiding under plants. I did a 50% water change, and she looks less droopy today. My husband said she was swimming about earlier, but was hiding again when I got home from work. She did attempt to eat.

One of my other mollies I think is pregnant and possibly about to have them. She's being a jerk and chasing around all the others really bad. She was attempting to hog all the food for herself (peas tonight). So that could be a possible reason for her hiding more today. pictures The first picture is the droopy tail. I don't have a picture of it looking worse. The second is the possibly pregnant one. Sorry for the quality, it's lights out for them and the pregnant one will not be still right now.

There's another mollie that does some minor chasing, but he only does it for like 2 seconds then stops.

29 gal tank, 6 mollies. Yesterday before the water change, testing was 0 ammonia, 0 nitrites, 20 nitrates, ph 7.6. Temp is 80. I added salt to the tank last week because I'm not sure if they have parasites or if I'm just paranoid. I've been also feeding them veggies every few days.

There's a possibility I put some fertilizer and/or Co2 drops on her. My fish are "starving" and start trying to nip for food every time I open the lid to the tank, even when I'm just using the eye dropper to get water for testing. So I've been putting it in the back opening for the filter. She likes to hang out in the water fall from the filter. I check to see if she was there before I dosed, but I after i was finished I saw her there. This happened the day before her tail started drooping. Is there anything else I can do for her?