Arowana can't see food

Kyungie

Feeder Fish
Apr 13, 2020
1
0
1
27
Hi all. I have a Asian arowana ~16 years of age, ~18 inch.
Diet: Superworms + Crickets (usually up to 18 per day combined)
PH: 7-7.2

Recently (6 days ago) I did a 20-30% partial water change. Usually he will only eat 2-3 days after the water change. (Water change done every 1.5 weeks)

Water change: Added water conditioner (anti-chlorine), some blackwater, Aquarium salt, some crushed corals in tank.

This time, his left eye seems to have a little drop eye and right eye is normal.
After water change:
3rd day - 3 crickets
4th day - 4-5 Superworms.
5th & 6th day - Can't find the worms.

It seems that he is unable to see his food well. On the 4th day, he took almost 30 mins to find the food while swimming aggressively.
May I ask what should I do to improve his condition and how to help him? Anyone tried hand feeding?
 
zoomed.com
hikariusa.com
aqaimports.com
Store