Two dead in as many weeks

[rg07]

Have lost a platy first now a gourami. But neither from the same symptoms. The platy seemed to be having problems swimming and would just rest on the bottom until another fish came too close. Then would wiggle away. But it was like her back was broken or something. It was like she couldnt swim correctly. This happened over a short amount of time and she stopped eating.

The gourami on the other hand must have had a disease of some sort. His fins were almost gone, so my assumption was fin rot. But we had only purchased him less than a week a go and was healthy. Eating, everything fine. Tonight he was curled up in a corner and weird transparent spots on him. Not black or white but spots like you could see into him.

All levels in tank are normal. Ph 7.9, nitrate 30, nitrite 0, ammonia 0, temp 77-79f

All other community fish seem fine for now. Gourami's, platys (except one is starting to exhibit same behavior as other platy that died), tetras, pleco,

Changed carbon a week ago shortly after getting the gourami, but the other gourami's purchased the same day were fine. Image is gourami prior to the spots showing up and finding him dead today.

Any help would be appreciated.