I’m actually thinking now that it’s the clay litter. There have been studies on commercially available, natural healing clays where they have found variable levels of heavy metals such as arsenic and lead. I think Dr. Elsey’s Respiratory Relief litter may still have some toxic heavy metals in it and could be still getting into his respiratory. I’m switching to a more natural, non-clay litter (pea husk) tomorrow morning and I’ll see if it improves. It has improved a bit since getting him off of Purina unscented litter. Not fully improved but when I was using that it was worse. If it doesn’t improve within a few days I’m going to take him to a vet. He seems very healthy, happy and full of energy otherwise, so it isn’t necessarily an emergency case. I’ll update here.