Can anyone identify the cause of death of my cory?

[Rachelcmartin]

Hi,

I have leopard corys and i've lost two suddenly overnight this week. Both with blood streaked scales and popeye. Does anyone know what this is caused by?

Water parameters: Ammonia 0, Nitrite 0, Nitrate 40ppm, ph 8, GH 17, KH 9. temp is 27c. Tank is 330 litres. Planted with bogwood.
Tank has been running for two months and before adding any fish it was cycled for 6 weeks using a fishless cycling method. All other inhabitants are fine I have ten juvenile discus, 6 white fin tetra and 5 leopard corys.

 

[Retired Viking]

@Colin_T

 

[Colin_T]

looks like a bacterial infection, the red is blood where the bacteria is eating the skin.