Algae belong to a seawater biotope as much as corals do. Only when algae start to take the upper hand do measures need to be taken against them. Because marine algae are very varied, it is best to explain how to deal with the individual marine algae.
Thread algae are no problem in small numbers. Indeed it’s good to have a few thread algae. They serve as food for algae-eating fish, such as surgeonfish, and they withdraw phosphates from the water. If they start to increase too dramatically the iron content of the water needs to be checked ( JBL Fe Test Set ). If you use a chalk reactor, check the water quantity passing from the chalk reactor to the aquarium. If it is too high, too much free CO2 will reach your aquarium and promote the growth of thread algae.
Sea grapes from the genus Caulerpa are very attractive but also have disadvantages. They are extremely fast growing and can, in doing so, overgrow and suffocate your invertebrates. They bind many phosphates and nitrates and are therefore cultivated in special “algae filters” where they are allowed to grow uninhibitedly. If the Caulerpas become too many they need to be partly removed. But be careful: If you “tear out” the algae strands, the algae cells will break and the cell juices with the once bound phosphates and nitrates will re-enter you aquarium water. Therefore please don’t have “big algae removal binges”, do it in small steps. This will prevent any negative side effects from occurring.
Brown algae (diatoms) form a thin film mostly on the substrate. They need silicic acid (SiO2), also called silicate, to grow. As soon as the silicate content drops they often disappear by themselves. If they do remain and multiply there must be a strong silicate source. Then you need to check your decoration material and also your starting water for silicates ( JBL Silicate Test SiO₂ ). For increased silicate values a special filter material JBL SilikatEx helps.
These very unpleasant looking algae mostly form when too many „reducing“ processes are taking place. Then the redox value decreases and the smear algae spread. A reduction of phosphate and nitrate mostly has no effect on the smear algae growth. Instead clean or replace the filter sponges, vacuum the dirt away from the bottom and blow off the debris under the decoration with strong pumps (and remove it with quick filters). After that the redox potential of your water will increase and the smear algae will disappear. The focus here is on the cleanliness of the bottom, the filter material and the decoration.
The first bubble algae look quite nice but when they begin to outnumber the invertebrates it’s time to think about combatting them. There is no “nostrum” except biological control. Many aquarium owners report of success with foxface rabbitfish (Siganus vulpinus) from the rabbitfish family. Some aquarists have noticed a connection between the algae and the potassium content of the water. After reducing the potassium content the bubble algae disappeared too.
We’re not talking here so much about combatting them, but about not letting them grow too well! Coralline algae look very decorative and a lot of aquarists like them. But they also grow on the panes and have to be removed by a powerful glass pane cleaner ( JBL Floaty Blade ). To make them grow vigorously they need the right calcium and more particularly magnesium values (Ca 440 mg/l, Mg 1200 mg/l). With the help of JBL MagnesiuMarin you can simply and professionally increase the magnesium level in your saltwater aquarium.