Dehydration is one possibility as is an infection, like Cat said. If that is not the problem, here's some ideas.
One is that the ammonia smell has been absorbed by the plastic litter tray, so even if you wash it, it is 'pre-loaded' for ammonia. On new litter boxes, you can somewhat seal the plastic with carnuba wax (or car wax) so the smells can penetrate and the urine balls stick less.
Adding another one or two litter boxes would help. The rule is one box per cat plus one for the house. With 3 cats, that's 4 boxes.
Different litters absorb odors differently. You could try changing the brand of litter you use to see if that helps. Some do have odor-absorbing crystals which can help.
_________________
"If a homeless cat could talk, it would probably say,
'Give me shelter, food, companionship and love,
and I will be yours for life!' " - Susan Easterly
|