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Article 21: Pond Water – Management, by Jeff Richardson

Posted by Jeff Richardson on

The main ingredient of the pond is water.  The water’s clarity, oxygen, chemical balance and volume are key.  Depending on the type of fish, wildlife and plants within will also determine how much you must fuss with it.

Losing Water: Routine evaporation, especially during the warmer months is normal.  As water splashes down the waterfall, some water is splashed out of the pond very slowly.  The water surface loses water vapor to the atmosphere especially when it is warm and dry out).  Even surrounding plants suck water from the pond.  However this amount of water lost in negligible (perhaps an inch or two in a week’s time).  But, if substantial water (4” or more perhaps over the course of a day), then it’s a sign that water is leaking out of the pond.  A clog in a spillway may be overflowing a component.  Another reason could be caused by a mole digging or erosion around the perimeter of the pond causing a low spot where the water is running out.  Lastly, it could be a tear in the liner (patch kits are available).  Fill the pond and components to max and turn off the pumps for 24 hours.  Check again for water loss (main pool: perimeter or liner; filter box: crack or drain valve not closed fully); otherwise waterfall course.  Note: To prevent complete water loss, install pressure switches in submersible pump housing or in the main pool to turn off pumps automatically. Beware of always leaving your autofill valve "on".  If so, pay attention to your water usage (using a meter).  The autofill valve could be masking a leak by keeping the water topped off!  Keep a weekly record of your water usage or use the valve in conjunction with a timer.

Adding Water: Use an auto-fill valve adjusted to shut off when it reaches full waterline.  Or, if manually, set a timer for a short period based on your flow rate and pond volume.  Depending on the overall size of your system, little or no treatment is needed for this small amount of water (otherwise add the prescribed amount of stress coat water conditioner which removes the chlorine and other chemicals added to tap water to make it safe for the flora and fauna).  NOTE: If adding bacteria, always wait a day after adding fresh water.

Clearing the Water: The water should be clear enough to easily see the bottom of the pond.  Should the water become cloudy or very dirty (such as when cleaning or disturbing the bottom), use the prescribed amount of clarifier.  If after a few days, there’s still no noticeable improvement, it may mean the filters are dirty or clogged (check and clean as needed) or the pump is not running at optimum flow (ensure they are clear and bypass lines are fully closed).  If algae blooms are at fault, use an algaecide.  If still no luck, consider a large water change (25-50%).  You will have to take care when replacing water with pond fish.

Monitoring the Water: There are a myriad of devices you should have to assist you in specific data about the water.  Get a floating thermometer.  This is key when deciding on winter shutdown (<40°), spring start-up (>50°) and seasonal feeding.  At the freshwater fill line, get a water timer and meter to allow accurate measuring of water added.  If during initial filling, you made a Staff Head Gauge, you will have an accurate pond volume by depth and time to fill or drain.  Test kits will allow you to see composition.  

Testing the Water: If the pond is operating at peak efficiency, the water will be clear; not cloudy or murky.  Algae will cover nearly all surfaces; but not excessive amounts.  The fish will be vibrant and active; not dull and lethargic.  There should not be a buildup of debris on the bottom of the pond and what debris there is should be breaking down quickly.  Aquatic plants should be thriving as well.  However, if this is not the case OR you have just completed excessive cleaning or large water changes, use a 5-in-1 water test kit which checks the levels of pH (Free Hydrogen Ions), KH (Carbonates and Bicarbonates Ions), GH (General Hardness – free Calcium and Magnesium Ions), and of course NO2 (Nitrites) and NO3 (Nitrates). If you have a large fish population, test weekly.  Keep test strips on hand and dry; avoid touching them.  Note: One-step glass vial oxygen saturation tests are available (DO).  Optimum: pH: 7 to 8.5, KH: >107*, GH: 107-446*, Ammonia: <0.1*, Nitrite: <0.1*, Nitrate: <50*, DO: >6* (*measured in ppm= parts per million).

Previous Article: 20: Pond Water – Nitrogen Chemistry

Next Article: 22: Pond Gear - Tools of the Trade

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2 comments


  • You are correct sir! Consistent and steady is best….and that is easier with larger volumes of water. As discussed in early articles about pool size, a small change in a small volume of water can cause great swings. A small change add to a massive water feature will not make a difference! It’s even harder to have temp swings in large ponds as the water gains and looses heat from the surface with the air versus all the water below.

    As for the test kits, I didn’t know about the strips expiration. I will note that! Yes, I have seen some liquid test and they are more pricey. The DO test kits I had seen in the past were like a chemistry set. Now, they have the one-step glass vials.

    Jeff Richardson on

  • Nice article Jeff. Thank you! A couple more suggestions on water quality.
    1) Consistency is key – it’s the fluctuations that stress the fish more than anything else. is the pH your water always at 8.5? while it may be considered on the high side, Koi seem like they can get used to it and still thrive as long as it’s consistent. same thing with temp – while koi thrive in the area of the 70-75ish degree range, if your temp is swinging more than a couple degrees per day this can be quite stressful for the koi even if it is in this optimal range.
    2) check your pH in the morning and evening. if there is a large swing, you’ll know it’s time to add some baking soda to buffer the water and/or it could be a signal to get your greenwater/algae under control
    3) Check your expiration dates on your test kits. I’ve known many test kits to start to give false readings after their expiration date. Don’t be fooled!
    4) Liquid test kits are generally considered more accurate than the test strips. However, they are also more expensive. It’s nice to have both on hand…

    Ben Cooke on

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