Is the baby ray meant to be smack under the bright lights? Sure that can’t be good in a hot tank where they don’t eat. If you have a working divider, why can’t you divide off the left 1 ft for example for the baby?
Just thoughts.
Seems odd your ph is so high. I would remove the conch and monitor to see if you get nearer 7. Do you have any other marine substrate in a filter or sump? Like coral or coral gravel?
Could freeze pop bottles full of water and float them in the tank to try to bring temp down. I also have to sit a fan on top of my tank with a built in led as the led unit heats the tank more than the heater does in summer. Maybe also keep the lights off more.