Cryptocoryne affinis is an aquarium plant less common - no particular reason why as it's a lovely Cryptocoryne and easy to grow. Olive-green to brown foliage only develops under water. Contrary to many aquatic plants, optimum growth of Cryptocoryne affinis is achieved in slightly alkaline water and therefore if you have a cichlid aquaria with limestone, it will do better in there.
That's not to say it won't do well in a typical acidic environment (it will) but just something to consider.
Understanding Crypt melt - all Cryptocoryne species require stable water parameter and light conditions. Once planted, Crypts should not be moved otherwise it can trigger what is called Crypt melt. If a Crypt has a significant change of environment (ph, kh , gh, lighting intensity or duration, root disturbance etc), Crypt melt can be triggered. The leaves start to disintegrate as the plant prepares for its new environment - DO NOT WORRY! Your plant will begin to grow back over the next 30 days (sometimes sooner, sometimes later) - it's still very much alive and busy getting ready for the growth of new leaves. In the meantime, any decaying leaves should be trimmed and recycled in a compost bin.