when i said rinse the media in aged water , i meant just the filter floss. I apologize if i didnt make that clear enough.
Cleaning the filter is very importannt with rays as i have had past experience where the water is kept pristine but the rays died because of high nitrates caused by dirty filters. We even have one member in here that lost a lot of rays because of the very same issue.
Without test kits, its really hard to determine what was the cause of the problem. Now that you have given us parameters, it is clear that the tank is "cycling" by the presence of nitrites.
How do you get rid of nitrites? Cleaning the filters and water changes?

Well even after all the water changes, today he came home to a ray laying on its back. My bro inlaw tells me the ray is still breathing but it looks to have what looks like to be burns in it belly and around its mouth it is very red. 



