Fish have scratches
My 4 Hoplosternum magdalenae have several white spots on their bodies, virtually overnight. They look like scratches or small injuries. Some of them are rather plain, others somewhat frayed. The shapes are also different (some are round, some are long). I think I can exclude Ichthyophthirius or a fungal infection. One of the four fish has some kind of opaque 'cap' over its eye, but nothing on the body. The behavior is fully normal; there is no scrubbing either. The Thorichthys meeki and the Ancistrus catfish are not affected.
it sounds as if the Hoplosternum got "in the way" of the T. meeki (possibly those were breeding or preparing to do so?) and got attacked. The description (uneven spots, looks like scratches, normal behavior) strongly indicate this. Treatment is not necessary in this case, just take care that no secondary infections occur (possibly you may use a mild anti-bacterial treatment such as liquid sera baktopur).
Dr. Bodo Schnell