Why did all four of my mollies die???

So I originally bought three mollies I brought them home that was about 4 weeks ago one of them died thought nothing about it I mean he got stuck to the filter a couple times but my betta has done that in his own tank and he's fine. I talked to the lady I bought them from she explained Molly's are really sensitive so I understood why he died getting stuck to the filter kind of stressful but I went and got two more they were balloon mollies I've had them for about 2 weeks and there is a dwarf baby frog a baby clown pleco and a juvenile pleco in that tank with them, it's a 40 gallon tank so I know they've got room and that wouldn't be the reasoning as to why they just all died but they've been perfectly healthy until I woke up this morning I got up around 6:00 to do a life check on them two of them were already dead so they had to have died in the middle of the night at some point I don't know when but I took their bodies out of it added some clean water into the tank around 9:30 to 10:00 in the morning I'd say the third Molly died and not even a half hour ago my fourth Molly just died so I'm wondering if I'm just not meant to have Molly's cuz I've had three goldfish a massive frog and a massive pleco living in a hundred gallon tank for almost 4 years and that's just whith the frog and the pleco the actual goldfish ive had in my care for almost 6 years I have a lot of single one of them I understand if it was like a Cold Shock cuz my room gets cold and I don't have a heater in there but I got a heater put it in there this morning around 9 to try and save the third one cuz I was watching him go that kinda crushed me so I don't understand why my last one just died cuz he was perfectly fine not even an hour ago but one of my mollies was white and he just had a yellow splotch on him I'm a little confused by that one cuz he didnt have it when I got him. I have never really had a problem with ammonia or any of that with any of my fish so I'm wondering if it's something I did wrong or if it's the fact that they could have been inbred with the fact that I litteraly got them from Ace but idk cuz all the research I keep doing is either leading to ammonia poisoning or loss of oxygen because they just randomly start sinking then darting to the top and when there stuck at the bottom and can barely go they start gasping, their fins are outward and going like they should like, but the fish looks like its almost fighting for his life I have never seen anything like this nor do I know how to fully explain it, it is just weird cuz I literally watched him go from being perfectly fine to dead in the matter of 5 minutes I'm so confused maybe its cuz the water wasn't hard enough I dont know I mean its tap water basically but there isnt any chlorine in it I put a algae control fluid in there maybe that's what did it but I know I didn't overdose them cuz that was days ago that I put it in so I don't know

Do you know your water parameters, especially do you have soft or hard water? Mollies need hard water and if yours is soft this could be affecting them. I imagine that balloon mollies are not very hardy, this seems to be the case with other deformed fish varieties. Other than those factors it’s difficult to know what is happening with them. What was the algae control stuff you added?

Fish don’t die because they get stuck on the filter. It’s the opposite : they get stuck to the filter because they are sick, and too weak to get away.

Fish don’t die because they get stuck on the filter. It’s the opposite : they get stuck to the filter because they are sick, and too weak to get away.

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Well darn I guess ace sucks for taking care of the fish or checking the background of where there coming from I dunno. Cuz i also got a betta from them and all the plecos I've got 3 plecos 2 frogs an 1 betta my 3 goldfish I got from a freind. Would it have been something I did possibly? It’s weird its never happened with any of the other aquatic animals I've had and the bettas fine he's just special in my opinion

Do you know your water parameters, especially do you have soft or hard water? Mollies need hard water and if yours is soft this could be affecting them. I imagine that balloon mollies are not very hardy, this seems to be the case with other deformed fish varieties. Other than those factors it’s difficult to know what is happening with them. What was the algae control stuff you added?

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Well my tap water is harder then heck it'll clog anything and everything with calcium the alkalinity is horrible but I bring water in for the fish I got told since they were with pleco's and a frog they'd be fine in the semi decent water and wouldn't need the hard water was that incorrect cuz if so I'll definitely ignore that source from now on and the algae control stuff was API Algaefix