Algae in RO Water Tank? Here Is What to Do!

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Algae in RO water tanks may sound like a rare occurrence, but it’s not as rare as it seems – especially if your water is supplied by a well.

While it may not be the most harmful contaminant out there, algae can cause issues if ingested, especially in larger quantities.

Let’s take a look at what to do about algae in your RO water tank, and how to prevent it from regrowing once you eliminate it.

Key Takeaways

  • Algae in RO water tanks is not the most common issue, but if your water is supplied by a well, then it has all the right ingredients for algae to bloom.
  • If you’re dealing with algae in your well water, then you’ll need to treat the well to kill off any algae growing in it. This can be done through shock chlorination – which is essentially pouring bleach down the well and running the solution through the entire plumbing system.
  • If your RO tank has algae in it – or you suspect that it does – the best thing to do is clean/sanitize the tank or better the entire reverse osmosis system. This involves pouring a small amount of bleach or another suitable sanitizer into the RO system and then allowing it to flush through.
  • To prevent future algae growth, make sure to change filters and clean/sanitize the RO system regularly. Also, store the system in a cool location away from direct sunlight.

What to Do If You Have Algae in Your RO Water Tank

Algae is an organism that naturally grows in water with warm temperatures and sunlight. It grows through photosynthesis, meaning it absolutely needs that sunlight in order to thrive.

Because RO tanks are opaque, sunlight cannot penetrate them and cause algae to bloom. So, if algae do find their way into your RO storage tank, it’s either coming from the water source or from within the reverse osmosis system.

Algae in the Source Water

Most of the time when you’re dealing with algae in your filter system, it’s because your water is supplied by a well. Municipal water is treated to remove microbial contaminants including algae, so if your water source is municipal you’re less likely to have issues with algae.

Wells are notorious breeding grounds for algae, as they have all the necessary ingredients for algae to thrive.

  • Wells are notoriously high in both nitrogen and phosphorous.
  • They also have higher pH levels, lower turbidity, indirect exposure to sunlight, and stable water with minimal turbulence – all conditions algae need to grow successfully.

If you’re dealing with algae in your well water, then you’ll need to treat the well to kill off any algae inside it. The process is called ‘shock chlorination’ and is used to eliminate a variety of potential microbial contaminants in wells.

algae with bubbles in water

To shock chlorinate your well:

  1. Add the recommended amount of chlorine bleach to your well, which will depend on the well’s diameter and depth.
  2. Use a clean new hose to run water into the well, making sure to hit the walls and circulate the bleach mixture.
  3. Rinse the well’s casing (the wall) for at least 10 minutes to remove any traces of chlorine.
  4. Now, turn on all of the faucets inside your home and run them until you start to smell chlorine. Also, make sure to run hot water to draw chlorine into the water heater.
  5. At this point, the chlorine solution has worked its way from the well into the pipes and fixtures in your home. Turn off the faucets and allow the chlorine to work for at least 12 hours.
  6. Now, run a hose outdoors until you no longer smell chlorine. Next, run each of the fixtures until you no longer smell any trace of chlorine.

Algae in the RO System

If algae are growing in the RO system, it means the system may be in a warm area exposed to sunlight. Because RO filters remove chlorine/chloramine – which kills algae – if algae do make it into your tank it can be an ideal environment for them to thrive.

Bottom line: If your reverse osmosis system is exposed to sunlight, you can relocate it to a darker and cooler area.

Where Does the Algae Come from?

Algae is like mold or fungus in that it’s practically everywhere, and only needs the right conditions to thrive.

Location: Why Does Algae Grow in Water Filters?

As mentioned previously, algae like relatively warm environments (68 to 86°F) with low turbidity and minimal turbulence that are exposed to sunlight. This is exactly what can be found in some water filters – which can make them ideal places for algae to grow.

How to Sanitize an RO Water Tank That Has Algae Inside

The cleaning/sanitizing process for a tank with algae in it is essentially the same as any time you need to clean your RO storage tank.

  1. First, turn off the feed water valve to your RO system.
  2. Turn on the RO faucet and allow any water left in the system and tank to drain out.
  3. Once all the water is drained, close the RO faucet.
  4. Shut off the tank valve on top of the storage tank and disconnect the tubing from the rest of the RO system.
  5. Add half a teaspoon of bleach (or another cleaner like hydrogen peroxide, chlorine, or tank cleaner) to the tubing using an eyedropper or funnel.
  6. Reconnect the tubing to the rest of the RO system and turn back on the tank valve.
  7. Turn on the feed water valve to let water back into the system.
  8. Allow the storage to refill which can take between 2 and 4+ hours.
  9. When the tank is full, allow the solution to soak in the tank for at least 30 minutes.
  10. Now, open the RO faucet and allow the tank to drain. Let the tank refill completely and then discard the second tank as well. At this point, no chemical smell should be left in the water, but if there is fill up another tank and discard it once again.

Keep in mind that your post-filter must be replaced after this unless you bypass it to avoid the cleaning solution.
Under Sink Reverse Osmosis System

How to Prevent Algae Growth in Your Reverse Osmosis Water Storage Tank Going Forward

  • The main thing you can do to prevent algae growth in your RO storage tank and system is to keep it in a cool dark place away from direct sunlight.
  • Other than that, make sure you’re changing your filter elements and membrane regularly according to the manufacturer’s recommendations.
  • Additionally, clean and sanitize the entire system every 6 to 12 months, which will kill algae and other microbial buildups.
  • Another thing to consider is adding a UV filter to your RO system. These filters are highly effective at eliminating over 99.9% of microbial contaminants including some algae.

Will Algae in My Drinking Water Cause Harm?

Algae are generally not harmful even when present in drinking water, although there are types that can cause health issues. Typical green algae are more or less harmless, while blue-green algae can cause skin irritation, respiratory issues, and hay fever symptoms.

Blue-green algae can also produce a toxin which can cause symptoms like stomach pain, vomiting, diarrhea, fever, headache, and tiredness.

If you have any questions about algae in an RO water tank please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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