Hystrix personality

Since I have had my trio there has been a lot of worry going on.

Basically they are either not as aggressive of eater as I am used to or there is something wrong. They spend 90 percent of the time buried in the sand and have really cut down on eating tremendously. To be honest if they are eating they are eating very little compared to what they used to. I am trying not to be paranoid but I kinda am. I actually bought some worms yesterday to get them eating (which they did) however for long term I am trying to figure out if this it the personality of this ray or there is something wrong

Water quality perfect and I drip 5gph on a 500 gallon tank and they have been in captivity for a few years now.

Tank mates are a bunch of rainbow fish, a few angels, and a tinfoil barb. Also an asian arrowana which is very non aggressive however wondering if this thing may be stressing them out.

I know not a lot of info to go on so just looking for a character reference on Hystrix. Are they active or do they hide a lot?

I will go out and get a nitrate test kit today and rule that out. With the drip I would find this hard to believe but you never know. The arrow does not touch anything in the tank however you never know maybe these rays just don't like it for whatever reason. Thanks for your help all...I will keep on slugging away and let you know. The rays did eat shrimp and smelts so I know it is a recent issue rather than a chronic one

Happy ending to this story. Moved the arrowana out (traded him for a BDXLeo) and now the rays are very happy and eating like crazy.

Also moved out my Rainbowfish while I was at it and went with 12 Tiger, 3 red hook and a regular silver dollars. Tank looks a bit more amazon now. Will post pics when things settle down.