German Blue Rams And Apistogramma

It depends on the size of the tank, and also the temperature. In smallish tanks - anything under 4 feet/120 cm long - the males of each species could well come to blows over territorial issues. In bigger tanks there should be enough room for both.

Rams, Mikrogeophagus ramirezi in all it's colour morphs and body/fin shapes, do better in temperatures in the upper 20's, while most apistos need round the 25 deg C mark. Some people find rams to be fine at 25 deg, but some individuals suffer at this temp. It depends just how long ago the last wild ancestor was - a lot of breeders introduce wild ram genes to widen the gene pool, and that could be quite recently.