What stops the process of diffusion across a membrane

The direction of diffusion is said to be 'down' or 'with' the concentration gradient. Diffusion stops when the concentration of the substance is equal in both areas. This does not mean that the molecules of substance are not moving any more, just that there is no overall movement in one direction.

Explanation:

if you are asking how much they can go over the 1500 limit it would be safetly within the 2310 and 2600.mg