Clarity, pH, & Hardness in Pond Water

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-Written by International Sales Manager, Joe Holz


Clarity issues can arise from a number of reasons, but no matter what the cause, the effect is cloudy water that is not as appealing as clean, clear water. While it may be an aesthetics issue, poor water clarity can actually have some benefits as well, such as blocking UV light that submerged plants require for life and thus, limiting some of the plant growth. However, most pond owners would prefer clean, clear water in their ponds.

Both organic and inorganic materials can lead to poor clarity. The most common organic materials are planktonic algae and suspended organic matter such as organic compounds that are in the pond or have washed into the pond from surrounding areas. Research shows that pond water that is properly aerated can actually improve the settling of these organic compounds faster than ponds without proper aeration. If the clarity issues are living planktonic algae related, a chemical treatment may be required to remove them from the water column.

Clarity problems due to inorganic material is often clay related. Clay particles are very small, which makes them ideal for pond lining because they stack together so much more tightly than sand or rock particles. However, being so small, it also means they can stay in suspension within a pond for a very long time. The best way to clear it up is using a flocculent such as Alum to bind to the particulates and settle them to the bottom. Flocculants can also help bind phosphorus to the pond bottom ridding the water column of nutrients that sustain algae growth.

Finally, clarity may be due to stained water. If you are in an area with high tree growth or your pond water source comes from areas with a lot of vegetation around it, you could have high tanic acid in the water which stains the water a dark brown, almost like root beer. There is very little that can be done to change stained water. It will be clean, just not clear. Stained water is not all bad though. It is almost like having free pond dye in your pond.


The pH level is a numeric value that indicates the relative acidity or alkalinity of the water on a scale of 0 to 14, with neutral at 7. Acidic water has pH levels below 7 and basic or alkaline water has pH levels above 7. Most lake and pond organisms prefer pH levels of 6.5 to 9. The pH levels in a given pond can fluctuate daily and is determined by complex relationships between carbon dioxide, hardness, alkalinity, photosynthesis, and respiration. If pH levels are not maintained, there could be negative effects in your pond.

Alkalinity or basic materials such as carbonates, hydroxides, phosphates, and bicarbonates are common in pond environments. Alkalinity is the buffering capacity of a pond or lake. This buffering capacity is important to allow pH levels to remain constant even with the introduction of acids from non-point source pollution and acid rainfall. Of pH levels are too acidic, lime is a common additive to bring the pH back to normal levels. Maintaining a healthy pH for your pond will help your pond organisms to thrive.

pH also changes throughout the day. As CO2 is released by plants at night, the pH lowers or becomes more acidic. During the daytime, as CO2 is used by plants, the water can become more alkaline or the pH raises. Buffering these pH swings using lime can help keep a more uniform pH level which will lead to better overall fish health.

pH can also effect bacteria and decomposition in a pond. Most bacteria cannot survive overly acidic water. Make sure to check the label, but if you pond is acidic, you may need to consider liming before bacteria treatments are started or at the very least lime to improve your resident bacteria populations.


Water hardness is the measure of divalent ions in the water. Some common causes of hardness are calcium and magnesium carbonate. If you go through a lot of salt in your water softener in your home, and you pond is in your backyard, there is probably a good chance you have hard water in your pond as well. Hard water can decrease the effectiveness of certain algae and aquatic plant chemical treatments. It can also limit the growth of plankton in your pond and limit fish growth.

There are not a lot of practical solutions to hard water in your pond. However, a pond manager may need to formulate the spraying mixture with different amounts of surfactants to properly treat pond weeds if you choose a chemical approach.

Showing 2 comments
  • Heather

    I have had ponds before, and aquariums inside my home with relatively no trouble for years. But we recently dug out a nice size pond, about 250-300 gallons. We filled it up, had good water levels minus the hardness (the water is hard in the city limits)and the PH was a tad high. We made the huge mistake of adding rocks, which turned the whole pond orange in a matter of 2 days, and resulted in a lot of fish loss, which was completely devastating.
    I took all remaining fish out, and set them up in a “hospital pond” (50 gallon pond that we had previously set up) for safe keeping, and drained all the water out of the big pond. I removed all of those dreadful rocks, and cleaned the pond liner before filling the thing back up (I treated the pond as I usually do for chlorine and metals with some Stress coat even though we weren’t putting fish in yet) and letting it sit, with the filter on, for a week. We had no problems, water remained clear, and welcoming.
    We don’t want to risk losing any more of our fish, they’ve been through enough, but we wanted to know if fish will do ok, so we got some feeder goldfish from the pet store, and figured we would give them a better chance than being fed to something.
    We know that not all of the feeders were in great shape when they came to us. Quite a few were swimming with difficulties even in the store- I tried to catch them as the guy was scooping, but I know we got a few sick water babies, which is sad, but nothing I could have done.
    They have been in the pond for 2 days, and we have lost about 3-4 of them. We bought 30 or so of them. I tested the water today, and it is Alkaline, and very hard.. What can I do to soften the water and bring the PH down to a level that is good for Koi, and goldfish?
    All the other water levels looked good; no ammonia, nitrates, nitrites.. Everything was in the recommended “safe zone” except the ph and hardness. How can I fix this?? I don’t want to lose any more fish!
    Ps. All of the ponds had high ph and hard water. I was able to use “PH down” inside, and in the little pond, but is there anything that treats this issue in ponds specifically?

    • Megan Wolf

      Hi Heather! Thanks for reaching out to us! Since pH changes throughout the day, it’s important to note at what time you’re testing. Do you know what the pH level was when you initially tested? Try testing at a few times throughout the day to get a better average. Please let us know if you have any questions. You can always give us a call at 715-262-4488. Thank you!

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