Is it possible to compute a simulation with OH- as primary species?

Dear all,

I would like to know if it is possible to compute a simulation by using a database with OH- as primary species. I used the kswitch utility in order to switch a database with H+ to OH- as primary species. However, the compution of pH seems to be stange. Perhaps CTOT in chemical file is not correct (I put in 'OH-' = 1.2589E-06 for pH=8.1).

In fact, I am trying to compute multiple restarts with a computation including surface complexation in alkaline environment. However, a each restart step, pH increases slowly (I do not have the same result without restart but the same final simulation time). I think that a problem can be the computation of h+ concentration, especially for small concentration. Another problem can be a restart problem.

Any idea?

Thank you

Anthony