Algae are actually something normal in the aquarium. Algae occur in very small quantities in every natural biotope. They only get out of hand if the conditions for the aquatic plants in the aquarium are unfavorable and the higher plants do not represent a strong competition for nutrients for the algae or if there is a nutrient imbalance in the aquarium.
Now and then an increased supply of phosphate is the trigger for algae plagues. Here there are special phosphate binders that flocculate the phosphate from the aquarium water. Bound in this way, the particles sink to the bottom and are removed during the next mulching.
Aquarium plants can only utilize nutrients depending on the light and the carbon supply (for example through CO2 fertilization). If, for example, the aquarium lamp is already old and no longer gives good plant light, the plants can no longer utilize the nutrients because they are limited by the weak light. The algae, which are much more frugal and need much less light, now take over, consume the excess nutrients and multiply excessively - an algae plague is born!
Another reason for the prevalence of algae is the opposite: you want to do something good for your aquarium plants and give them one of the new powerful LED aquarium lights. Now there is a lot of light in the aquarium, but no additional CO2 and no additional nutrients. The algae master biogenic decalcification, so they can produce carbon from the hydrogen carbonate that is always present in the water. Most aquarium plants cannot do this. Thus, the algae can use an alternative carbon source and really thrive under the extra light.
It is always best to optimally coordinate the nutrient supply, the CO2 supply and the light. This strengthens the plants and gives algae no chance to take over the aquarium.
Sometimes, however, for example with freshly set up aquariums or with a stubborn algae plague, you can no longer really get around an algae killer. Here in the online store you can buy algaecides from renowned companies such as JBL, Aqua Tropica, Sera and Aquasan Attention! In planted aquariums with shrimps, please only use algaecides that have been explicitly labeled as safe for shrimps. Most anti-algae agents contain copper, which would be lethally toxic to shrimp! It must be explicitly or at least analogously "safe for shrimps" on the package if you want to avoid unpleasant consequences for your little crawlers.