While algae are a nuisance but some alga are worse than others. Black Beard Algae (BBA) has got to be one of the worst. Most algae problems can be avoided with frequent water changes and careful nutrient dosing schedules. Not the case with BBA.
The best way of avoiding BBA is by using CO2 injection. The CO2 appears to prevent the growth of BBA. However, if you do not have a planted tank, then CO2 injection just for the sake of preventing algae may seem overkill.
Seachem Excel has long been known to act as an algaecide. While not intended for this purpose, many have used it in an attempt to rid a tank, once and for all, from the dreaded BBA. However, the results vary greatly. The reason for this is simple. The active ingredient in Seachem Excel is dilute glutaraldehyde. The glutaraldehyde is only capable of killing alga upon direct contact. Therefore, just overdoing a tank with Seachem Excel will not kill the BBA. In order to do that, you have to remove the equipment, ornaments, wood, rocks, plants etc. that have BBA on them and apply the Seachem Excel directly to the BBA. You can do this using a small syringe. Leave the object/plant out of the water for at least 10 minutes, before placing it back into the tank. Over the next few days you should observe the BBA turning red before falling off.
It is important to note that if you apply the glutaraldehyde directly to plants you will experience some die off. However, there is no need to panic. Most hardy plants, such as Anubias sp. and Java Fern can withstand this kind of harsh treatment. In general, the plant will lose some of its leaves and seem to be struggling before bouncing back about a week later.
If the Black Beard Algae is growing on the glass of the aquarium, simply drain the tank and then, using a syringe, apply the Seachem Excel to the exposed area. Wait 10 minutes before filling the tank back up again.
This does not only work for BBA. It works for all types of algae!