what's wrong with my pleco's fins?

[flowerhornfishman]

so, this issue has been almost a month now and it never healed or even infected any fish.
his fins are somehow like been ripped off or maybe been eaten by bacteria? i dont know. maybe it's an injury done by my snakehead(which i already removed) about a month ago and still hasnt healed yet.
here are some pics,

 

[Aquanero]

Please post your water parameters ammonia, nitrite, nitrate, ph and hardness if available. How often do you do tank maintance, water changes, substrate vacuming and filter cleaning?