stressed

hey i have a 9.1 gal tank and i brought 4 mollies today 3 females 1 male all the females are pregnant. i put them in the tank and they seem very stressed they swim up and down not really fast but normal speed i done nitrate and nitrite test they were both 0 ppm i added some aquarium salt didnt...

I came home today and my swordtail in my 29g tank had a black line down his body. I had never seen it before. He was also acting droopy, hiding and not swimming a whole lot. There is nothing wrong with any of my other fish and swordtail. there isn't anything else on him beside the line if...