When attempting to compute a model using the Multi Species Extension (MSX), the following error occurs:
Could not solve reaction equilibrium expressions.
The error is mentioned in the "EPANET Multi-Species Extension User's Manual" on page 112:
Error 514: could not solve reaction equilibrium expressions.The nonlinear equation solver employed by EPANET-MSX could not successfully solve the system’s set of equilibrium equations at the current simulation time. Users must insure that the initial conditions set throughout the pipe network are sufficient and consistent so that a solution exists for the governing set of equilibrium equations.
Another situation that has been known to cause this error is when using negative demands (inflows) in particular on the upstream side of a tank. In these cases, either explicitly model the source, or add the negative demands directly on the tank node.
Using Multi-Species Extension (MSX) for advanced water quality modeling