Staghorn algae grows in individual, short branching strands that appear greyish-green in colour. Their branching formation looks a bit like antlers. Staghorn algae usually grows along leaf edges but can appear on hardscape as well.
It’s usually caused by high levels of ammonia and excess organics, and will favour stressed, unhealthy or old plant growth. Low levels of pressurised CO2 will also encourage Staghorn algae to grow.
If your tank is still cycling, your ammonia levels will be high - this can’t be avoided without disrupting the process. Wait for your filter to establish its beneficial bacteria and observe the algae to see if it subsides on its own.
If you have an established aquarium, start by cleaning your filter if you haven’t done so recently. Siphon any detritus from your substrate and perform a 50% water change (this should be done weekly).
Plants and leaves can be misted with hydrogen peroxide or the whole tank can be treated easily with products such as LCA Carbon Plus or Triple B. Spot dosing or full tank treatment will help slow the spread of Staghorn, or weaken the algae so it can be more easily removed by hand or algae eating livestock.
You can also completely remove any affected growth completely to stop the algae from getting a foothold. Healthy, unaffected plant growth can be replanted.
If you’re using pressurised CO2, consider if you are injecting the correct amount into your system and adjust if necessary.