Since it's in the control , l suggest you use algaecide. Normally algae are bioabaorbents.

Controlling algal growth in phytoremediation experiments using polluted water can be challenging, but there are several strategies you can employ to help prevent excessive algal growth in your control pots:

1. Shade or Cover: One of the simplest methods is to provide shade to the control pots. Algae require sunlight for photosynthesis, so shading the pots with a mesh or cloth can reduce their access to light. This can help suppress their growth.

2. Reduce Nutrient Availability:

a. Nutrient Monitoring: Algae thrive on nutrients like nitrogen and phosphorus. Regularly monitor and adjust the nutrient levels in the control pots to keep them at a minimum.

b. Nutrient Adsorption: You can also add materials like activated carbon or zeolite to the control pots to adsorb excess nutrients, reducing the availability of these nutrients for algal growth.

3. Algaecides: Consider using algaecides or algistatic chemicals that are safe for the environment. Copper-based algaecides, for example, can be effective in controlling algae, but be cautious about their potential environmental impacts.

4. Mechanical Removal: Periodically scrape or manually remove algae from the control pots. This can be a labor-intensive method, but it can help keep algae in check.

5. Biological Control: Introduce aquatic animals that feed on algae, such as certain species of snails or small herbivorous fish, into the control pots. These organisms can help control algae populations.

6. Biofiltration: Consider using other plants that can outcompete algae for nutrients and resources. For instance, emergent aquatic plants like water lilies can shade the water and outcompete algae.

7. Maintain Water Quality: Ensure that the water in the control pots is well-aerated. Algae can proliferate in stagnant water, so maintaining good water quality and circulation can hinder their growth.

8. Regular Monitoring: Continuously monitor the control pots for algal growth and adapt your control strategies as needed. Make sure you are not inadvertently introducing nutrients or contaminants into the pots through any external means.

9. Sterilization: Before starting a new experiment, you can sterilize the pots and growing medium to remove any pre-existing algae and microorganisms that might contribute to algal growth.

10. Controlled Experiments: Ensure that your experimental design is well-controlled. The presence of a confounding variable may inadvertently promote algal growth.

Select the method that best suit your specific experimental conditions and goals, and be mindful of the potential environmental impact of any chemicals or biological controls you use.