I am looking for an easy Hypertufa recipe to make bird baths and such.
Don't listen the cashier. Don't add anything to the water. Cats are smart. They like plain water and it keeps the kidneys functioning normally.
I recommend keeping up with the brushing. Just be patient with them and they'll adapt to it. They may never be thrilled about it, but they will become more accommodating. IMO, nothing should replace brushing as a standard practice for helping to maintainin good dental health.
After our cat developed gingivitis, we began to use a dental kibble which has done wonders for her oral health. Our vet agrees. Because she also has a kidney issue, we mix it half and half with a low ash kibble.