I had my former horse Red develop Anhydrosis. Ugh. It is a nasty condition. I tried EVERYTHING. A special recipe, Equiwinner Patches, One AC, Guinness Beer everyday.
The special recipe seemed to help the best. Equiwinner Patches not at all. I rehomed Red and they gave him barley which helped. That is what is in beer of course. I had to rehome him from that home and he is sweating somewhat but not great. I had the pleasure of having his new owner ride with hubby a few weeks ago.
I had an extra batch of Equiwinner Patches and sent them recently to a lady near Houston Texas when her horse stopped sweating. Thankfully she said this helped her horse and he was back to sweating. Doesn't work for all horses.
When I rode Red I hosed him off BEFORE riding him and scraped him off. I kept water to pour on him and a sponge to drop in any creeks we crossed and rode him right into the lake at times. At home, I kept him where he could get into a stall or walk at into a paddock at will. A fan on in his stall during the summer. He actually sweats normally during about 9 months out of the year. I would go to the barn and hose him off several times a day too.
Sorry you are having issues and if you would like the recipe of salt/sugar I gave him let me know.