First time post, if I'm in the wrong spot please let me know. Considering this is "beginner" I figured this is where I should post. I started out with a small 5 gallon fish tank at work, with a buddy that works there that's big into fish that got me more heavily into the fish keeping hobby. I picked up a 30 gallon tank for at home, sadly I started stocking this ~2 weeks after setup before I realized how important cycling was. A mistake I won't make again. I originally started with 3 small painted platies and had them for a week and then dropped 3 balloon mollies in with a bristlenose. All was well up until 4 days ago. One of my balloon mollies (memo) was literally fine before I went to bed and when I woke up it looked like she was having swim bladder issues lying sideways at the bottom of the tank, 3 hours later she was dead. I did a water change of about 50% after her death. 2 days later before I went to bed a platy was not moving a whole lot and I got a bit worried and did a 30% water change, next morning he was dead as well. Today... my other balloon Molly was acting a bit slow this morning, and now about an hour ago she was dead as well. I did another 30% water change and tested and still found no issues with The water. The 3 remaining fish seem to be active and okay. I've tested the water 4 times so far, with the 6 in 1 test strips and all the readings come out as either 0 or in the "safe" zone. Am I doing too many water changes? I'm conditioning the water for chlorine that has added stress coat before adding it in. Water looks clean, and with the initial water change after the first death I did a gravel clean. I'm pretty sure one of the balloons (the one that died today) was pregnant, there have been about 7 fry surviving in the tank for ~5 days now. I'm afraid I'm going to see my active fish go from fine to dead in no time if I can't figure out what's going on.