The reverand is correct, you temp is high. Most recomend 72-75 for most tropical species of SH. I keep mine on the low end 71-72. Sh are highly suseptable to bacterial infections, and the higher temps raise the risks. There is also a very small treatment window with SH. MOst newer hobbiest miss the symptoms and don’t begin treatment soon enough.
Aippis, can be a huge problem in a SH tank. Often, you may not see a wound but the horse devolops a bacterial infection from it.
Is there any way you can put your horse in a hospital tank? If she is going to require any meds. you will need to. Slowly over a 24hr. period drop the temp to 74. If she is sick 69 would be better.
MAybe Pete will come along and help, I’m affraid I’m not much good at the how and why of it.
Best of Luck