The link didn't work for me.
If the fish is darting around and acting aggressive or mean, it could be toxic water quality.
Do you have your water parameters?
If not, can you do a few water changes? If the water changes seem to help, do a few more!
25% then another 25 % wait an hour if it seems to help, then do 2 more back to back water changes.
If the fish seems better then you know what's going on. Do a 50% water change and the next day do another one.
Get a test kit, or see if you can get the water tested for free at a local store. Write down the water parameters for each thing they check and tell them you need to write it down ahead of time.
What size is the tank?
