Wierd Platy Behaviour

Hi all,

Last month a female guppy started losing colour and started getting bent out of shape. A couple of weeks later she died. I put it down to old age since the water parameters were perfect. We then left for a holiday for a week and when we came back there was a thick black spot under the sand. I noticed one of my female platties was missing so on cleaning the sand substrate, bits of her body started surfacing up. There were loads of snails feeding off her. Not sure how she got into the sand. Now the last 2 female platties are behaving the same way. They are hanging out in the same place where the other female platy's body was found. At first I thought they were pregnant, however, now I've noticed the other fish pecking at them. I'm not sure what the problem could be. Could it be some disease in the tank? I don't want my fish dying. My water parameters read 0 ammonia, 0 nitrite and 50-80 nitrate. Please help, it looks like the other 2 platties are going to die too. I have attached a pic of them both hanging out in the same spot the other platy died. Please advise

50 - 80 nitrates!?!?!? What kind of test kit are you using? If your using a good one and these levels are correct your nitrates are wayyyy to high!

The fish look very thin, they could be suffering from internal bacterial infection, but fish TB is also a posibility if the fishes spines are bending. Do any of the fish appear to have inflamed/sore looking anus? If so then internal parasites are to blame for the fishes condition.
Your nitrates are also pretty high, how often are you doing water changes and how much are you taking out on average? Do you have any unhealthy looking plants or dirty substrate in the tank etc?

I would start by doing a 30-40% water change, waiting an hour and testing again, if the nitrate is above 30 ish I would do it again, until its really 10-20.

As Tokis said before, check for rotten plants or if you feed vegetables check theres none lay around the tank.