This is a species that raises a lot of questions. It was first described in 1912 but was never properly identified in the hobby. All of the early information about ortmanni actually refers to a stendachneri group fish that was commonly thought to be ortmanni. In 1985 the first photos of true ortmanni were published in Germany. Since that time there has been better info available about this regani group fish. However, there is still a lot of confusion surrounding the various populations of this fish and there are three or four recognized forms. All are relatively subdued in coloration and do not have elaborate finnage. Most of the fish in the regani group are similar and there remains a lot of work to be done to determine the exact relationships.
In terms of aquarium care treat them like any Apisto. give them good water, good food and good habitat and they should thrive. They shouldn't be too demanding of water conditions fairly soft slightly acid water should be fine. In nature they are found in a variety of water types ranging from full black water conditions to moderate conditions.
A. ortmanni are not common in the hobby as they lack many of the spectacular colors and shapes of some Apistos. This creates less demand as most hobbyists seek the more colorful species. However, they should be a great fish with interesting behaviors. Good luck with them.