The short answer
Staghorn algae forms stiff, grey-green branching tufts that look like tiny antlers, usually on leaf edges, filter outlets and hardscape. It’s a classic symptom of unstable CO2 and poor water flow. The fix is to improve circulation, keep CO2 steady, and spot-treat the tufts with liquid carbon while you sort out the underlying conditions.
Improve flow and CO2 stability
Staghorn takes hold in dead spots where water stagnates and CO2 levels swing. The goal is even, gentle circulation so every plant gets a steady supply.
- Boost flow. Angle your filter outlet to push water across the whole tank, or add a small circulation pump. Clean a clogged filter that’s lost pressure.
- Stabilise CO2. If you run pressurised gas, keep it consistent through the photoperiod rather than spiking. See our CO2 systems for injection and diffusion gear.
- Balance light to CO2. Too much light with too little CO2 is a staghorn trigger — trim your photoperiod to 6–8 hours if plants can’t keep up.
Spot-treat the tufts
Staghorn is tough and algae eaters largely ignore it, so treat it directly. With the filter off for a few minutes, use a syringe or pipette to dose liquid carbon straight onto the tufts. Over a few days they turn red or grey and die back, after which you can pull or syphon them out. Repeat during water changes until it’s gone.
Keep it from returning
Once the algae is cleared, keep conditions stable: steady CO2, good flow into every corner, a photoperiod on a timer, and weekly water changes to keep nutrients balanced. Staghorn shares its causes with black beard algae, so if you battle both, read what eats black beard algae and our full how to get rid of aquarium algae guide.