Reaction-diffusion equation pollutes domain with extremely small solution

1

I run a 3D reaction-diffusion equation with diffusion parameter = 0.6 and reaction parameter = 0.25 to solve a tumor evolution model. The initial condition is a gaussian hill in the middle of my domain, with a=1 and b=3, setting the initial tumor
When I run the simulation, after t = 0.001 the whole domain (box 181x217x181) has a solution of 1e-100.

Is there a way to set the solution values to 0 if they are below a certain threshold or am I having another problem?

2

There is no way of telling if you are doing something wrong without a minimal working example. For guidelines of creating a minimal example, see: Read before posting: How do I get my question answered?