mikrogeophagus ramirezi

I have 2 tanks, 40G & 75G. Small one just has 18" long pleco, big one has 6 discus fish in it. I bought 12 Hemigrammus erythrozonus & 10 Mikrogeophagus ramirezi. In which tank should I put them? I was planing to add tetras to pleco & rams to discus. But now I second guessing what if pleco will...