Salt is not a solution ?
Have you seen kitchen salt? Did it look like a solution do you, or was it a white solid?
Detergent is not a solution?
In general detergent is a substance. It can be dissolved. Such a solution is sometimes called a detergent too. Such a name is way too ambiguous to allow any specific conclusions.
Cod liver oil is not a solution?
To some extent it is, but - to make things more precise - pH is well defined only for water solutions. It doesn't make much sense for other solvents, oil included.