Sometimes if the coat has been cut short it will either change color or get fuzzy or curly from the waist down. I don't know the reason for this but it happens. I would suggest you use a very mild doggie shampoo even if you have to add water and dilute it down. Next and very important at keeping knots out and making brushing easy is to apply a really good conditioner. What I do is this.........I mix a little JoJoBa oil (probably about 10 drops)with #1 ALL SYSTEMS conditioner AND...MATRIX BIOLAGE hydratherapie OR PANTENE Nourishing. With cotten coats that matt easily, you have to be aggressive with the conditioner.
In the summer they get a hot oil treatment after their shampoo and before their conditioning, once a month. In the winter, I give them the hot oil treatment once a week after their shampoo and before their conditioning.