No the eye happened before the water quality issue, but one one eye that got injured, thats why i dont think its the water. All polys seems ok and doing fine.Sponge filter would be useless as it wouldnt be cycled. Use the airline to create some wster current if you dont have a spare filter but the sponge would be better served sittong in the sump cycling. Did the eye thing start when you noticed the water quality issues ?
I had basically the same thing happen to my delhezi, I just kept up water changes, cleaned my filters, added some salt, and added some melafix. Went away in a few days