Not knowing much about Corydoras, but I graduated in Chemistry, I would be very carefull with ferteliser

Regardless the formula, plants need potassium, nitrogen (that is, ammonia, nitrites nitrates) and phosphates. Further they will need some trace minerals, such as copper, selenium iron and ...

Those cloudy eyes are weird. There are several different causes of cloudy eyes. Reportedly, low pH can cause it, and also some parasites. Your pH is on the high side. I don't know if high pH can do it too.

Maybe something with the ferts? I don't use fertilizers in any of my tanks, so I'm only ...

This is a problem that has plagued my Bronze Cories for many months now, and no one has even the faintest idea what is happening. I don't think it has any environmental cause, but I know it's important to establish the environment these guys are in.

1. Water parameters
a) Temperature range
74-76 F ...