There are two classes of heterokontophyta that are often referred to as brown algae. The first is class bacillariophycaea (the second, phaeophycaea will be discussed later.) These single celled diatoms are usually seen when a tank is first cycling within the first couple of weeks or so. They reproduce extremely quickly; it is possible to thoroughly clean your aquarium in the morning only to find it completely covered again by night.
This is a normal occurrence and not something to be particularly concerned about or frankly even bother with trying to control at first. Luckily this fairly unattractive specimen can be easily managed and doesn’t usually last long after the initial cycling period.
The amount of silicates in your water (this can vary depending on the source of your water) will determine how much you will see. The diatoms need to consume silicate in order to grow. If you can avoid adding new silicates to the aquarium, the growth will discontinue and they will eventually disappear. Kalkwasser (limewater) is a popular calcium supplement used to maintain a high pH in the reef tank. Using this when replacing evaporated water can quickly control the growth of diatoms (more discussions about kalkwasser later.) A large infestation of diatoms usually results in a large amount of waste being emitted into the water by the algae. It isn’t advisable to introduce livestock into the environment until it is under control. Common methods of filtration (protein skimming, carbon, ozone, etc.) will reduce their ability to reproduce and their waste. While it’s likely to always find a certain amount of diatoms in any aquarium if you look for them, in small quantities they aren’t harmful.
