What is the foot print of this 60 gallon? I would think that you'd have to pass on the Hecqui, all fish in the Lepidiolamprologus genus are quite pugnacious, I wouldn't mix them with any other shell dweller. How long have you had the Metriaclima Livingstonii (previously Ps. lanisticola)? They can get pretty aggressive as well when they reach maturity, but I can see them getting along with the brevis. As you know the convict will eventually become a problem, but if you want to keep another shell dwelling species I suggest you try caudopunks or Altolamprologus compressiceps "Sumbu", depending on the foot print or course.