My water tank is 100 gal or 120 gal I think it's 120 gal but obviously that's not enough in this hot weather. I live on the gulf coast and I can look out almost any day and see my horses all sweated up just staning in the pasture grazing! I have not even thought of ridding it's just to darn hot.
Also please check your worming program. Parasites are a huge factor in most colic cases now days. Even if you are worming are you switching products and are you POSITIVE the horses all get a full dose??
Good luch and i'm very sorry for your losses.