Missing eyeballs
 

I have a 29 US gallon freshwater tank with the following:
1 black ghost knife
4 neon tetras
5 black neon tetras
4 tequila sunrise guppies
3 red wag platys (1 male, 2 female)
2 otos
1 spotted cory catfish

Three of my black neon tetras are missing their left eyes. Who would you
suspect??? I have moved the injured tetras into a hospital tank. I
removed the carbon in the filter and am treating with a slightly elevated
dose of sea salt plus some anti-fungal and anti-bacterial medicines from
my fish first aid kit. Surprisingly they have survived 3 days in this
state and are active swimmers.

I definitely need a new home for my knife; he is already 6 inches long and
will reach a mature size of 18 inches. He is blind (like all his
species), has a playful personality, and generally leaves the other fish
alone (he does guard one cave with tail and fin nipping).

TIA,
Laie Techie