it was a new tank with new sand staight from the sac. I installed a new HMF in the guppy tank but that tank was uneffected till I threw in the loaches and roselines form the new bottom tank when they started to float and act wierd .
ther is nothing that close by that could have caused issues .iv had tanks in this corner of the house for 18months with out any issues . I think it was the sand, probably cross contaminated like other have mentioned before.
I was just shocked how quickly the cories started to react to whatever came in from the bottom tank with the loaches/roselines, iv never killed a tank so quickly and completely .