Large predator fish

Hey guys hoping you can help me out. I came came home to my parents for the week (I live 8 hours away) and always help my dad with his tanks. One of them is a 125 gallon tank with subdued lighting and live low light plants. Filtration is 2 emperor 400s, a whisper 60 and a cascade 120 canister. Tank has been up for 3+ years at this point. Not much in the tank accept for a couple syno catfish a shovelnose and a jardini arrowana. The jardini has been alive for well over a year at this point and was started in a 55gallon as a 2-3inch juvie (now about 12inch). He always ate very greedily live goldfish and all sorts of pellets (shrimp and cichlid pellets).

Now the problem, he has not ate in 3 weeks! He one day just stopped eating anything tried pellets crickets and goldfish he just goes to the bottom and lies there until you go away and everything else in the tank comes to eat the food. I decided to test the water andthe pH was 6.8 ammonia was 0 no nitrite kit and the nitrates were high (80) which i think is due to the large gravel and the canister filter.

Any suggestions? The guy ate like a pig beforehand so he does not look real slim or unhealthy at this point but I am not sure how much longer he could starve out like this

 

Try some water/filter media changes, get the nitrates down a bunch.

Hope that helps.

 

have you tried fresh foods? like live fish? I think it also may be time soon to move him to a new tank since they're usually suited to 250+ I think 125 may be getting a bit small...