I’ve been keeping large fish for a long time—arowana, bichirs, datnoids, big cichlids, you name it—and one thing I’ve learned is that tanks rarely “crash out of nowhere.” The fish almost always show signs first. The problem is that the signs are small, and most of us ignore them until things get serious.
I wanted to share some of the early warning signs I’ve personally seen over the years. These apply to big, high-waste fish that need more attention than the average setups.
I wanted to share some of the early warning signs I’ve personally seen over the years. These apply to big, high-waste fish that need more attention than the average setups.
1. Fish Hanging Near the Surface
If your fish suddenly start hanging around the top, moving less, or breathing heavier, it’s usually an oxygen issue or parameter spike. Big fish suck up oxygen fast, especially in warm tanks. Check your aeration and water movement.2. Cloudy Water Even After a Water Change
Cloudy water in a larger tank is almost always a filtration issue. Either the bio-load is too heavy or the filter isn’t keeping up. When I used to keep two oscars and a big pleco in a 90, my water never stayed clear until I added more mechanical filtration.3. Reduced Appetite
Large fish don’t randomly stop eating. If your fish suddenly shows less interest in food, something is off—stress, parasites, or unstable water quality. I’ve had datnoids go completely pale and stop eating when nitrates got too high.4. Sudden Color Changes
Color shifts are one of the clearest stress indicators. Darkening, fading, washed-out patterns… it’s their way of telling you something’s wrong.5. Random Aggression
If your normally calm fish starts chasing tank mates, it could be responding to poor water, temperature swings, or territory stress. Aggressio is often a symptom, not the root problem.6. Gasping After a Water Change
If you’ve ever done a big water change and your fish suddenly look stressed or start gasping, it's usually from temperature or pH differences—or chloramine not being neutralized properly.How to Stay Ahead of Problems?
This is what’s helped me avoid disasters:- Test water weekly, not just when something looks off
- Don’t overfeed—monster fish are messy
- Upgrade filtration as the fish grow
- Use strong aeration and surface agitation
- Match temperature and pH during water changes
- Keep backup equipment
