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How to Prevent and Remove Red Algae in a Fish Tank: 9 Expert Tips

Chris Dinesen Rogers

By Chris Dinesen Rogers

Red Slime Algae

Algae is a natural component of aquatic ecosystems. However, it can be unsightly in a tank or deadly if it occurs in the wild. Red algae contain cyanobacteria in its cellular structure. Like algae, it uses photosynthesis to produce energy. Freshwater tanks or water bodies are more likely to have the blue-green form, though.

An aquarium overwhelmed by red algae means you have an unbalanced system. Therefore, the steps you must take involve restoring it. Each one has prevention baked into the plan, which we’ll point out along the way.

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Before You Start

Red algae is more harmful in nature than in your aquarium because there’s more fuel to the fire with the factors that cause it. Nevertheless, it’s imperative to control the problem as soon as you notice its occurrence. It can proliferate rapidly and take over a tank. Of course, prevention is always preferable to any issue of this scale.

Don’t be tempted to make drastic changes to your aquarium because of red algae. It’s imperative to minimize stress while you’re getting rid of it. You may need to mentally prepare to lose a fish or two in the process. However, stay focused on the end game, which is creating a healthier environment for your fish.

Materials you’ll need for this task include the following:

  • Water test kit
  • Siphon
  • Bucket
  • Replacement filter cartridge
  • UV clarifier
  • Live plants (optional)
  • Algae eaters (optional)

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The 9 Tips on How to Prevent and Remove Red Algae in a Fish Tank

1. Run Water Quality Tests on Your Tank

holding PH tests in front of freshwater aquarium
Photo Credit: M-Production, Shutterstock

While red algae are a visible problem, issues also exist with water quality. That makes testing essential to determine if you’re making progress. Consider it your baseline. It can also give you valuable info for knowing when your aquarium is entering the danger zone. One of the main causes of red algae is an overabundance of nutrients and the resulting waste.

  • Prevention Tip: Do bi-weekly testing as part of regular maintenance.

2. Siphon the Substrate During a Partial Water Change

A partial water change will help restore the conditions back to normal by reducing the organic matter contributing to the issue. You should use a siphon to clean waste from the substrate. Try to cover as much of the bottom as possible, moving hardscape features as necessary to get the bad stuff out of your tank.

  • Prevention Tip: Make this task a regular part of your maintenance to cover all the bases.

3. Replace the Cartridge on Your Filter

Photo Credit: Igor Chus, Shutterstock

A clogged cartridge can impede water flow and contribute to poor water conditions. It can also reduce the amount of dissolved oxygen that is necessary for the health of your tank. A dirty cartridge can make your filter work harder than it should and threaten its lifespan. Don’t wait until you notice a reduction in water flow.

  • Prevention Tip: Set a reminder on your phone to stay on schedule.

4. Adjust the Lighting in Your Tank

Remember that cyanobacteria can conduct photosynthesis in the presence of UV light. However, we must return to balance. That includes lighting. It’s also a way to stop red algae in its tracks if you go dark for a few days. No UV light means no photosynthesis and the energy it produces. It’s not the prettiest way to control it, but it is effective.

  • Prevention Tip: Put a timer on your hood light to stick to a regular lighting schedule.

5. Fine-Tune Your Feeding Schedule

Photo credit: hedgehog94, Shutterstock

An abundance of organic waste sets up the perfect storm for red algae. You’ve likely noticed the feeding instructions on any fish food you buy saying to add only as much as your fish will eat within a few minutes. Take these instructions seriously. They will get used to the regular schedule, which will make your job easier. It will also help you gauge what is the correct amount to offer.

  • Prevention Tip: Follow the instructions on your fish food packaging to the tee to determine the needs of your fish. Measure the food if necessary.

6. Use a UV Clarifier to Remove Excess Algae

You can remove red algae manually. However, we strongly urge you to use gloves in case they contain toxins. However, it’s a disruptive process if your fish are still in the tank. A UV clarifier minimizes the stress they will experience. Copper is also effective but can be harmful to some species. This option eliminates those risks.

7. Retest Your Water

testing water pH
Image Credit: Warakorn Buaphuean, Shutterstock

You should repeat the battery of water quality tests after going through this process. It will help you gauge the effectiveness of your efforts. It can also provide fodder for tweaking your maintenance schedule. You may be pleasantly surprised to learn how well you’ve done in restoring balance to your aquarium.

8. Rinse and Repeat

If things aren’t right, we suggest repeating these steps. It’s far better to take the slow road than rush through the process. It’ll be much easier for your fish, even if it means more work for you. We suggest monitoring the health of your fish throughout the process to make sure they aren’t overly stressed.

9. Consider Adding Live Plants to Your Tank

angelfish in planted aquarium with Cryptocoryne Balansae
Image credit: vbmark, Shutterstock

Live plants can provide formidable competition for red algae by competing for precious resources. Thankfully, they will likely have a competitive edge. That can be enough to keep the nuisance at bay. After all, they must have sufficient nutrients to survive and proliferate. Think of it as beating nature at its own game. It works, as simple as it sounds.

  • Prevention Tip: Monitor the health of your plants to ensure they aren’t adding to the organic waste load.

10. Bring in a Cleanup Crew

Algae eaters and catfish aren’t going to eat red algae. Instead, they will act in a similar role as live plants by adding competition for resources to the mix. Your aquarium is a closed environment, limited by what you add to the water. Stepping up the game is an excellent way to control the problem in a non-invasive way.

  • Prevention Tip: Keep your clean-up crew well-fed with blanched vegetables or algae wafers if they’ve blown through the algae.

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Final Thoughts

Red algae may not be the correct descriptor, but the point is well-taken. It doesn’t belong in an aquarium, even if the conditions make it inevitable. Several steps can help you get it under control with minimal effort. Those methods work because they also reduce stress in your aquatic environment. Remember that a tank is closed and inert. Regular monitoring is vital to ensure stability and algae control.

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Featured Image Credit: Joe Belanger, Shutterstock

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