too much lye wont hurt.. too little would..  add plenty, till colour turns completely back, then add some more

pH papers are useless in STBs, you cant really read them as the colour of the brew stains the papers (you could measure a solution before adding MHRB but the pH will change once there is something else added.. dont know how much it changes though)...  But yeah in any case the important is to know that too much lye wont hurt, might only help (like preventing/breaking emulsions, guaranteeing dmt is in freebase form, and breaking down mimosa further for helping releasing dmt)