Alkali metals and viscosity

I've recently conducted a viscosity experiment to find the relationship between alkali metal ions, the concetration of the solution, and the viscosity of the solution. We used the Oswald viscometer to determine the viscosities of $(\pu{0.5 M}, \pu{0.25M}, \pu{0.125M}, \pu{0.0625M})$ solutions of $(\ce{LiNO3}, \ce{NaNO3}, \ce{KNO3})$, and found that the while the viscosities of the $\ce{LiNO3}$ and $\ce{NaNO3}$ solutions increased as the concentrations of their solutions increased, the viscosity of the $\ce{KNO3}$ solution would instead decrease. 


And so we ask:


1. What is the relationship between the viscosity of a alkali-metal nitrate solution and the variant of the alkali metal ions within?
2. Why would the viscosity of the $\ce{KNO3}$ solution decrease with concentration?


