Algae is very hardy and can be really tough to remove from the fish tank, especially Black Algae (BBA). The main cause is the phosphate and other nutrients which are generated from left over food.
There are very few fish that will eat this algae. SAE’s and Yamato shrimps are known to eat it but they may not be enough if BBA is well established in your tank.
Total blackouts may not work either as this algae is not caused by extra light but fundamentally, an excess in nutrients. Frequent water changes are strongly recommended during any treatment. Adding more plants, especially the aggressive and fast growing “floaters” such as Pistia, Salvina, Duckweed to absorb the extra nutrient quickly, may also help, remember if the algae is in “bloom” …. It is still in the initial stage.
There are many views on how to remove the algae and some people recommend manually scraping off the algae from the leaves as they believe that this is the best way to get rid of these ugly additions to your tank. Before trying this or any other “radical” treatments, always seek advice. If your tank is infested with BBA, reduce feeding immediately and you may also need to stop any fertilisation and CO2 injection as well.
It can be tough fighting these unwanted guests and you must ensure that you are careful with any treatment; it is feasible that if you approach this in the wrong way, a complete aquarium revamp could ensue. As with many things, prevention is ALWAYS better than cure, as soon as you see the first signs of BBA, add extra plants (floating plants) and assess what could be causing your particular issue.