Whether your aquarium glass is turning green, leaves are covered in fuzz, or the water has taken on a soup-like appearance: green algae in an aquarium do not point to a single problem. A light presence is a normal part of tank life. However, a proliferation that hides the decor, hinders the plants, or accompanies water degradation deserves investigation into its cause.
To act effectively, first identify where the green is located: in the water, on the surfaces, or in the form of filaments. You can then combine cleaning, input control, and appropriate adjustments.
Three situations not to be confused
| What you see | Useful check | Action to consider |
|---|---|---|
| Green water throughout the volume | Observe a sample against a white background | Look for a proliferation in suspension and check clarification |
| Film or spots on the glass | Compare a small cleaned area to the rest | Clean with a compatible tool and monitor the rate of return |
| Threads on plants or decor | Photograph the surfaces and affected areas | Remove the filaments and examine growth conditions |
A slimy layer that detaches from the substrate requires a different check. Consult our guide to slimy aquarium deposits before treating it as mere filaments.
Start with the condition of the fish and equipment
Observe their breathing, swimming, and appetite. If the animals show abnormal behavior, immediately check the temperature, filtration, and relevant water parameters. The green color alone is not enough to explain their condition.
Check the flow at the outlet, the cleanliness of the intake strainer, and the operation of the heater. A filter can still make noise while circulating less water. Check for clogging or a hose problem before considering a replacement.
Once these points are checked, you can organize your actions against the algae. Keep a record of measurements and interventions, especially if several people maintain the tank.
Why do algae thrive during certain periods?
In a newly installed aquarium, plants are adapting and biological filtration is establishing itself. This phase requires gradual adjustments. A proliferation can also appear in an old tank after changing a lighting fixture, increasing feeding, or significantly modifying the decor.
Possible causes combine: abundant light, nutrient input, accumulated waste, and plants that are growing poorly. Therefore, it is rarely useful to choose a single explanation based on the color of the algae.
Look back at the previous weeks. A timer stuck on manual override or a ration doubled by mistake are concrete elements to correct. This observational work avoids adding a product without understanding what has changed.
Check the actual lighting of the tank
Note the start and end times, but also look at the daylight. An aquarium can receive several hours of direct sun before its light fixture even turns on.
Check the programming and any automatic modes. For a new planted aquarium, Tropica suggests an initial duration of six hours daily during the first weeks in its startup protocol, then a gradual adjustment. This reference concerns that specific context; it is not a universal setting for all tanks.
Also adapt the intensity to the plants. Strong light requires consistency with other cultivation conditions. Increasing CO₂ or fertilizers without a diagnosis to "keep up with the light" can create other difficulties.
Measure nutrients without systematically aiming for zero
Nitrates and phosphates participate in plant nutrition. Monitoring them allows you to examine inputs and consumption. In a planted aquarium, the goal is not to blindly eliminate all elements necessary for the plants.
The JBL ProAquaTest CombiSet Plus NH4 includes nitrates, pH, KH, nitrites, and ammonium. Add a phosphate test if this measurement is useful: it is not included in this kit.
Compare the tank water and fresh water when the source of an input remains uncertain. Respect the reaction time of the reagents and note the units. A result should not be interpreted solely based on a photograph of the color scale.
When can an anti-phosphate product be relevant?
The JBL PhosEx rapid is a liquid treatment designed to lower excessively high phosphates in a freshwater aquarium. Its presence in a maintenance program must be justified by analyses and the tank's needs.
Consult the current instructions before use and plan a follow-up check after the intervention. If the source of the input remains active, the problem may return. A corrective product therefore complements research into food, fresh water, and waste; it does not replace this research.
Clean surfaces with a compatible tool
For the glass, choose an accessory suitable for glass or acrylic. A grain of sand stuck in a pad or magnet can scratch the wall. Clean the tool and avoid dragging it against the substrate.
The biOrb pads are designed for the acrylic walls of biOrb aquariums. For any other material or fragile decor, check the recommended usage before scrubbing.
Remove loosened waste and heavily degraded leaves during maintenance. For filaments, our guide dedicated to filamentous algae details a step-by-step approach.
If the water itself remains green
Fine mechanical filtration can retain some matter, but it must be monitored to avoid clogging. Check that the flow remains sufficient and that maintenance does not simultaneously destroy the filter's biological media.
A suitable UV-C clarifier can be considered against organisms in suspension. It must correspond to the volume, circuit, and flow rate recommended by its manufacturer. It does not directly illuminate algae fixed to leaves or stones.
Before this purchase, get clarification on the type of cloudiness and your setup. A UV device alone does not correct excessive feeding, poorly adjusted light, or an unsuitable population.
Choosing an algaecide with the right checks
The JBL Algol is a reference for freshwater aquariums. Its use requires reading the current label, calculating the actual volume, and checking the organisms present. JBL warns of possible sensitivity in dwarf shrimp and certain mosses.
Do not consider the mention "copper-free" as a guarantee of universal compatibility. Maintain the oxygenation conditions required by the instructions and plan to remove the degraded matter. A treatment does not replace correcting the conditions that favor recurrence.
Build a sustainable routine
Choose a few reproducible checks: lighting programming, distributed rations, outlet condition, surface maintenance, and appropriate tests. The pace depends on your aquarium, but consistency facilitates comparison.
Evaluate the speed at which algae return after cleaning, not just the immediate appearance. Slower growth and recovering plants are useful information for adjusting the next steps.
To establish an appropriate plan, contact the Aquiflor team with the volume, population, lighting, measurements, and a photo. You will be able to select the necessary tests and equipment without multiplying blind purchases.
Sources and useful reading
- Tropica: distinguishing green water, filaments, and surface deposits.
- Tropica: gradual adjustments when starting a planted aquarium.
- JBL: precautions regarding Algol and shrimp.
- OATA: water control and aquarium maintenance.
- Aquishop product sheets linked in the article.
