Who Gives A Fish Forums

I've got a group of 6 Discus in a 75-gallon tank, and they've started chasing my Cardinals and Rams. Water params are good, 0 ammonia, 0 nitrite, nitrate around 10ppm. Temp's at 84°F, pH 6.8. They're fed twice daily with a mix of frozen bloodworms and beef heart. Anyone know why they're acting like this?

Sounds like territorial behavior. Discus can get aggressive if they're establishing a pecking order or if the tank's overcrowded. How long have they been in there together? Also, what's your decor like? Hiding spots can cut down on stress.

Mine did the same thing when I added new tankmates. Took about a week for them to chill. Maybe they're just not used to the Cardinals yet. You got any driftwood or plants for cover?

Yep, it's usually a dominance thing. My big male Discus used to chase everything until I added more hiding spots. Now he's too busy exploring the caves to bother the others. Try adding some tall plants or rocks.

I've got a similar setup but no issues. Maybe it's the beef heart? Heard it can make them more aggressive. Try cutting back to once a day.

Tonito wrote: ↑Wed Jun 25, 2025 10:41 am Sounds like territorial behavior. Discus can get aggressive if they're establishing a pecking order or if the tank's overcrowded. How long have they been in there together? Also, what's your decor like? Hiding spots can cut down on stress.

Agreed. Also, check your lighting. Too bright can stress them out and trigger chasing. I run mine on a dimmer schedule now.

Mine were fine until I added a new filter. The increased flow seemed to sketch them out, and they started chasing. Maybe check if anything's changed recently?

It's likely a combo of factors. How old are your Discus? Juveniles are usually more chill, but adults can get territorial, especially during breeding. Also, what's your water change routine? Consistency matters.

Thanks for the tips, everyone. I'll try adding more plants and maybe tweak the feeding schedule. Appreciate the help!

Had the same problem last year. Turned out my Discus were just bored. Added a couple of floating plants and some dither fish, and they stopped chasing. Worth a shot!