Most Crenicichla come from very soft acid and mineral-free waters. Polypterus species come from very hard alkaline mineral-rich waters. Some poly species can do OK in pH neutral conditions. But, IMO, that pH is still outside the comfort zone of most Crenicichla species.
well, what are some species of pike that get between 6-10"? i don't think a bichir can eat a 6" pike, i mean they don't have the mouth of a gulper cat or a leaf fish.
you could go with a Saxatilus sp like Sveni, Belly crawler, Lucius etc. Def can do Lugubris pikes (get over 10") like Johanna, Cincta, Xingu (I, II, III), Strigata, Venezuela etc.
the 4" one i think might be too small, so the menezesi seems like the way to go. my water has a PH of 7.6, but is somewhat soft, so idk if a pike would enjoy it or not.
also are menezesi's very common? also, would this guy do well in a 40 gallon breeder with a delhezi bichir and a leopard ctenopoma?