Are you feeding a lot of high fiber foods? The white droppings are usually called urates...I see them sometimes after soakings or if I surprise the with a special treat like watermelon or pumpkin..but they've never been hard. They look hard after they dry up but usually they are somewhat runny.

The soakings are good--I would recommend lots of grass and weeds and maybe back off of some other foods if they are on commercial diets or salad mixtures...but another vet visit may be what you need if he's still not passing and eating like normal.

With the weather getting cooler it is common for them to slow down a little but I still find mine eating like they did before. Heat should be provided when the temps start to drop.