Controlling algae in the aquarium

Algae have been naturally present on earth for millions of years… without them, life as we know it would become impossible. Even a perfectly clean looking river or lake contains algae (but too much would be a sure sign of imbalance and could harm wildlife). Leave a glass of water in your garden for a while and sooner or later algae will invite themselves in, as spores can travel in the air.

That being said, it is a completely different problem when it comes to an algae bloom, which not only makes the aquarium unsightly but also makes maintenance cumbersome and kills beautiful plants!

In a newly set-up aquarium (less than 6 months old), as water parameters are not fully balanced yet, it is common to find quite a lot of algae. Once the tank balance improves, ideally, they should remain under control and should only be present in small quantities.

You will find below a series of tips to keep algae under control and to keep your plants healthy:

• Install the aquarium as far away from direct or excessive natural light as possible (otherwise, a sheet of black paper/cardboard can be glued to the side of the aquarium that receives sunlight);
• Grow plants in your aquarium, if possible fast-growing plants to start with. Plants compete with algae and absorb excess nitrate and phosphates. Without plants, only algae benefit from these nutrients, which can lead to their proliferation. You can consult our plants section for a selection of plants suitable for goldfish or any freshwater tank.
• Avoid overcrowding or undersized tanks: this translates into a high concentration of nitrate and phosphates, which are used as food by algae. For the same reason, do not overfeed your fish.
• Regular water changes can prevent excessive nitrate and phosphate build-up. A change of 10% or 15% per week is better than a change of 20% to 30% per fortnight. However, the tap water must not itself contain too many nitrate and phosphate to start with. If this is the case (often in areas where agriculture is intensive), you can use a phosphate removal media in one of the compartments of your filter.
• Inject CO2: Insufficient CO2 concentration harms good plant growth, which indirectly encourages algae growth. Click here for a beginner’s guide to CO2 in the planted tank (external link).
• Use good quality lighting and adjust the lighting duration: 8 to 12 hours maximum per day is more than enough in most cases. Lighting should be adapted to plants (power + light spectrum): for example, strong lighting for slow-growing plants with moderate light requirements will inevitably benefit algae; conversely, if the lighting is too weak for your plants, they will die or grow poorly… which will still benefit algae.
• Add “algae-eating” or “glass cleaning” fish: these fish are supposed to graze on recalcitrant algae. Important note: be careful when you choose algae-eating fish, as some unscrupulous sellers do not hesitate to sell some species of locarids, which once adults, become huge ‘monster’ fish of 50cms or even a meter long! So unless you invest in a fish tank of several hundred litres, these fish will undoubtedly have a cruel end. Also, check before any purchase that the algae-eating fish you want to buy is not territorial or aggressive, as well as the temperature and pH compatibility. In doubt, visit a fishkeeping forum or get a fish book before committing. Please note that some of these fish are faithful allies while others can gradually become interested in plants (especially if algae are in short supply), or will only be interested in algae when they are young. Or will increasingly turn to artificial food, accessible without much effort, intended for other fish.
• Clean the areas where they grow regularly with an algae scraper or toothbrush.
• Anti-nitrate or anti-phosphate resins significantly reduce the concentration of these two substances but do not address the real causes of the problem. However, if the problem is caused by the excessive presence of nitrate or phosphates in tap water, then this can be a good option (another one being the use of osmosis water, which will then be re-mineralized).
• Using chemicals is generally not recommended because it is a short-term solution and can sometimes damage plants.