My Precious Fish Are Dying

[joselaz5780]

So about 4 days ago, I had my platy girl give birth and it had 15 healthy babies. I washed the breeding net well since it had a couple of months without use and inserted the babies inside of it. The babies are slowly dying one by one and yesterday my swordtail died. The swordtail was only about 8-9 months(It was born in my tank). Today my adult platy which was about one year(also born in my tank!) died. These two deaths got me extremely upset and sad since they happened out of nowhere and they both died one day after the other. Right now I am out of test strips and will not manage to go to the store until tomorrow or a couple of days... I did a 50% water change, cleaned filter media and decided to give less food than the usual. I have also been changing about 10% water every other day for about one year now and the tank has been doing well, that is, until now. So, what the heck could be going on here?! Also, when the swordtail and the platy died, they both went between the glass and breeding net and turned upside down. The swordtail's tail also broke apart before death. Please help? I have 3 more platies which were born in my tank and I have grown to love them and I also have 5 3 month old babies which are hanging with the big guys too and I don't want them dead. My cories have been doing well, so that's good.