Mustard Algae or Sand?- Here’s How to Know (With Pictures)

Mustard algae and sand are two sworn pool enemies. What’s worse is sometimes they can be indistinguishable from each other. Mustard algae has a yellow granular appearance that can easily be confused with sand, pollen, or dirt.

If you have ever experienced a swimming pool covered in strands of greenish yellow slime, you can understand how unpleasant it can be. This could happen due to poor water circulation, not enough sunlight, or low chlorine levels. Most of the time, it is the chlorine resistant mustard algae.

And then there’s sand, an age-old foe to pools. Once you’re down in your pool to relax, it can come across shocking, and intruding. Keeping these two pool buggers in mind, read on to know how to differentiate between them. As once you’ll be able to tell them apart, only then can you have them shift their humble abode from your pool.

How to Differentiate Between Mustard Algae and Sand?

The biggest problem associated with mustard algae is its misdiagnosis which leads to the escalation of the situation. It is pretty easy to confuse mustard algae with sand or pollen given its yellow color and granular appearance.

Starting from the base, algae are microscopic plants that need light, oxygen, and nutrients to live. Most of the algae in swimming pools grow at the water’s surface. Mustard algae are chlorine-resistant algae that can often be seen at the bottom of pools.

Sometimes, you may even think that your pool is dirty- little do you know, you could have an algae infestation. Luckily, there are a few ways to draw a line between these two.

Brush Test

This is one of the simplest tests you can perform yourself even at a tiny area in your pool rather than testing your entire pool. All you need to do is clean the patch tiles thoroughly with a dedicated pool brush and then wait 12 to 24 hours.

We highly recommend a dedicated work boot, like the Ever Boot Ultra-Dry work boot, for any procedure that involves entering a wet pool for your own safety. You can also choose from our list of Best Pool Cleaning Shoes.

If the patches reappear, you do have algae infestation. Whereas, dirt or sand will accumulate at the base of the pool.

Another thing that you should notice is if it gives you any trouble in brushing off the dirt. Sand does not come off easily and usually requires a detergent or a leaching agent. Mustard algae, on the other hand, can be brushed off pretty easily. We have a complete guide on How To Test For Mustard Algae? here.

Be aware of the position

Unlike sand or dirt particles, mustard algae does not accumulate on the bottom of the pool. It is usually found on the walls, in patches. Sand ,on the other hand, is found in the form of a layer at the bottom and walls of the pool. 

Sand accumulated at the bottom of a

Mustard algae at the bottom of a pool- Reddit

Texture Test

One of the easiest methods to differentiate algae from other impurities in your pool is the texture test. Scrape some of the yellow material from the walls of your pool with a pool brush and rub it between your thumb and index finger. If the texture is brittle, it is probably dirt or calcium scale. If it feels slimy, it may be algae.

Mustard Alage, with its almost sand-like appearance in a pool.

Mustard Algae, giving a granular and sandy-like appearance, on the staircase of the pool- Reddit

Observe Your Walls

Mustard algae take some time to grow initially, but once the growth has initiated situation can escalate rapidly. Most the people don’t know that algae are a living organism that grows. It climbs the walls whereas dirt, sand, or calcium scale do not. To delve into even further detail, read: What Does Mustard Algae Look Like?

Check Your Chlorine Levels

This is one of the most important confirmatory tests. All you need to do is check your pool’s chlorine levels and leave it overnight. Recheck the chlorine levels in the morning.

If the difference In both measurements is less than 1ppm, the chances are that it is just sand or regular dirt. However, if the difference exceeds one ppm, mustard algae might be the culprit. You will, however, need an accurate digital pool test kit for this which will help you throughout life in maintaining your pool’s chemistry.

Jar test

This may seem like going beyond the edge, but you can never be too sure. What you need for this test is a transparent jar. Scrape some part of the patch and put it into the jar, then place your jar in a ventilated and shady place for a few days.

After a few days, if you observe that the patch has grown, it is most definitely mustard algae. If not, it could be sand or any other substance. 

How To Get Rid of Mustard Algae?

Shocking is the textbook methods to get rid of mustard algae or any other kind of algae in your pool. For someone who’s never done it, it can be a tricky process.

To shock your pool correctly, you need to begin by thoroughly cleaning your pool walls, skimmers, stairs, pipes, any pool equipment, swimsuits, toys, etc. Doing all this helps to prevent your pool from getting contaminated again. 

Since mustard algae is resistant to chlorine, you need to triple shock your pool (1.5 kg/ 40,000 l of water). The purpose is to sustain chlorine levels of 25-30 ppm for several hours. We have found these HTH chlorinating tablets particularly effective in this case. Keep brushing your pool for several days regularly after that.

Also, keep the pool stabilized adequately during this period for maximum efficacy. This step is optional, however. You may use the Pool Mate stabilizer for the task.

The best time to shock your pool is when the sun has gone down. It allows free chlorine to attain its maximum concentration. After shocking the pool, keep the filter running for the next 24 hours until all the algae has been cleared. 

Sometimes, mustard algae may survive even the pool shock. In that case, you might have to use algaecide or chlorine enhancers. You can use algaecides while shocking your pool, or you can use these separately as well. Clorox pool algaecide would be an excellent choice.

How To Get Rid of Sand?

Getting sand out of your pool isn’t rocket science, but it takes some work. The best way to remove sand is to vacuum it up. Here are the steps you need to take:

  1. First, you need to overfill your pool, so even if your vacuum ends up sucking some of the water out, you’ll still have an appropriate water level.
  2. Brush off the walls and pile up sand in one place. 
  3. Now, quickly vacuum. You don’t want the sand to scatter. A fast hand-held vacuum like the Kokido Tesla 5 definitely helps ease this step.

How To Prevent Mustard Algae In Your Pool?

Algae growth is usually associated with human errors such as improper chlorination, clogged basket, etc., but mustard algae can grow even with impeccable pool cleaning. Mustard algae often grow during rain or are introduced from lakes, ponds, or leaf rakes. Here’s how you can prevent it:

  • Clean the pool equipment, toys, filters, and ladders as well. 
  • Monitor the phosphate levels in your pool, keep it under 200 ppb. You can also use a chelated, broad-spectrum, copper-based algaecide. 
  • Make sure to keep the filters running for 8 to 10 hours every day.

How To Prevent Sand In Your Pool?

The simplest and the most obvious way to do this is to cover your pool with a dedicated pool cover. This prevent entry of sand in the first place.

Some of the pools use a sand filter; a higher than normal levels of sand can lead to leakage into the water. If despite a sand filter, you see the level rise and disrupt your pool peace, then you might need to check it out.

The sand filter might be cracked or malfunctioning. Installing a sand filter and keeping it running like a pro is key to preventing sand in your pool. You can also try switching to EcoPure filters if your filters are the suspect.

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