How To Keep Algae Out of Your Pond - Crystal For Beginners

23 March 2013  |  Admin

How To Keep Algae Out of Your Pond - Crystal For Beginners

Clearing green algae from your pond can be very rewarding. A clear sparkling pond can be a source of pride and joy in your garden. The key to achieving success with Hydra Crystal is test, treat, and Filter, Filter, Filter!

It is very important that you read all the guidelines supplied with the product before treatment. The key one being oxygen requirements for your fish. To read more about oxygen click here.

We strongly recommend conducting a preliminary glass test before applying the product to your pond. Residual chemicals can prevent the product from working, so the glass test will show us if the product is suitable for use in your pond.

Step 1. The Glass Test

  • Stir water up from the bottom to make it representative of the entire pond and take a sample of water out into a half pint glass.
  • The first check: is the water green? If it is, add a pinch of crystal to the water, just like a pinch of salt.
  • Leave the sample to stand overnight. This test will tell you if you have the right product.

After 24 hours, what has happened to the water? If your water has cleared in the glass then proceed to the next step.

See our Crystal in action within minutes of being added to the green water. As you can see, it is safe to use in your fish pond. 

If the test fails and your water doesn’t clear, the product is not the right product for your pond. The minerals in Hydra Crystal have not coagulated the pond algae.

VERY IMPORTANT: Only apply the product to your pond if it clears in the glass! Your glass is your pond in miniature. If you are unsure call our customer services team.

Step 2.Treating your pond

Calculate the volume of water in your pond. Click here for our pond volume calculator.

1kg of Crystal will treat up to 10,000 litres of water. To calculate how much product you need to use, you can utilise the following equation:

No. of litres in your pond / 10,000 = X kg.


If your pond is 6ft x 10ft x 2ft = 3398 litres (using the pond calculator)

Using the above equation: 3398/10,000 = 0.34 kg or 340g
1 level scoop of Crystal is 20g 340/20 = 17 scoops

Treat your pond in late morning to early afternoon. Click Here for oxygen requirements needed in your pond.

Make into a slurry by taking a small container of TAP WATER (do not use pond water) and mixing the correct quantity of Crystal with the water. This is not an exact science, making into a slurry aids distribution throughout your pond water.

Pour into your pond at the pump outlet for maximum mixing within the pond.


Step 3. Filtering out the Algae

In order to achieve a fully clear pond the dead algae needs to be filtered out. Crystal will clump the algae together, and then it is the role of your sponges to filter these algae out.

This step relies on your filter system doing this effectively. The denser the sponges in your box, the quicker the water will clear. Pond Filter Blankets filters down to 20 microns. This is very small! If you do not have a blanket, there are other options available such as Japanese matting etc. Coarse sponges that only filter out solids, gravel filters and filters without a mechanical filtration element will not be sufficient to filter out the fine, clumped, dead algae.

After a few hours of treatment, check that your filter is capturing the algae. You must continuously clean your filter sponges in order to remove the trapped algae.

The speed in which Crystal works will depend on the flow of water through your filter and the efficiency of your sponges to trap the fine algae particles.

Suggestion: You can cut our pond filter blanket to size and use it in place of one of the coarse sponges in your filter. This can be easily removed and cleaned throughout the treatment.

In time, after successive filter cleanings, your pond will clear.


What happens if my pond does not clear?

There are only two reasons why your pond has not cleared:

  1. You haven't used enough of the product (check dimensions and calculations – we can help you with this)
  2. You have not successfully filtered out the dead algae.

To check if the filter is adequately filtering the dead algae out of your pond water take a sample of water out of the pond and leave to stand overnight.  Does the water clear? If the water clears in the glass but still hasn’t cleared fully in the pond, this shows us that you have used the right amount of product but you haven’t filtered all the algae out. Continue to circulate the water and clean your filters, the addition of a pond filter blanket at this point if you don’t have one would be highly beneficial.

Another way of checking if your filter is trapping the algae sufficiently is to take a sample of water from the filter outlet and compare it to the sample from the pond. If there are bits/algae particles floating in the water in the sample from the outlet, we know that some of the dead algae are still getting through the filter.


Step 4. Re-treating your pond

If your pond water is very green, you may need to re-apply again. You can re-apply after 48 hours if the pond is not clearing. We suggest you conduct a partial water change of between 10-20% of the pond water between treatments.