So sorry
What temp is the tank at? Looks like they can handle up to 85, it probably is better to keep temps no higher then 80-82 long term I’d think.
If it were my tank I’d have a rotation of frozen water bottles ready to go. If you don’t want em floating in the tank add it a hob filter without the media. I’ve used those blue ice cooler packs on a couple occasions before I had central air in my house. Just slid em in the filter and switched it out every few hours. Worked pretty well until the house cooled down at night.
Sorry to hear you lost one of the little guys. Make sure to keep increased surface agitation if your tanks run hot to keep the oxygen levels up.