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WATER QUALITY - KH, pH, AND ALGAE

Frogs love decreased water clarity, but you may not.Carbonate Hardness (KH) and Acidity (pH) are two very important water quality factors involved in establishing a healthy balance. These values are interdependent and greatly influence the performance and health of plants, fish, and beneficial micro-organisms in your pond.

Pond pH changes throughout the day, starting at its lowest point in the morning and increasing throughout the daylight hours. Photosynthesis during the day increases pH, and plant respiration during the night decreases pH. This is called a diurnal cycle. The ideal value for most ponds with goldfish or koi is between 6.8 and 8.2 with a fluctuation of no more than .8 per day. When there are excess nutrients and/or the pH is high, algae thrives. When algae thrives it usually keeps the pH high (lots of photosynthesis) which makes it difficult for the plants in the pond to compete for pond nutrients.

High pH can stress fish, inhibit plant growth and curb the beneficial functions of bacteria and other microscopic organisms in your pond. Some types of algae have a much greater tolerance for high pH, doing quite well, while fish, scavengers and other plants are struggling.

Carbonates buffer or moderate pH so that it swings less and does not get too low or too high. The ideal carbonate hardness is 125 - 180 parts per million (ppm). Tap water in our region tends to have a very low KH and typically needs additional buffering before the pH will stabilize in a healthy range.

Test the KH (buffering capacity). Once the KH is within range, adjust the pH. When pH and KH are in the ideal range, everything does better but algae!

Adjusting the KH in your Pond
Follow test kit directions to determine your KH. Note: The result may be expressed in ppm or dh (degrees of hardness). Multiply the dh value by 17.9 to find out how many ppm of carbonate hardness. [7° dh x 17.9 = 125 ppm ]. If the value is at or more than 125 ppm (7° dh), that’s usually very good. If less, increase the carbonate hardness.

Criteria for usage:
If the KH is less than 125 ppm or if pH changes more than 0.8 points per day, treat with sodium bicarbonate (Baking Soda).


Ideal KH = 7° - 10° dh or 125 - 180 ppm [dh x 17.9 = ppm]

To raise KH, add sodium bicarbonate and retest after 6 hours. Continue to treat until you have a reading at or above 125ppm.

Application Rates for Sodium Bicarbonate to increase KH

Conversions for Sodium Bicarbonate

Pond size
100 gal
250 gal
500 gal
1000 gal
10,000 gal
30ppm
.7 oz
1.8 oz
3.6 oz
7.2 oz
4.5 lb
40ppm
1 oz
2.4 oz
4.8 oz
9.6 oz
6 lb
50ppm
1.2 oz
3 oz
6 oz
12 oz
7.5 lb
75ppm
1.8 oz
4.5 oz
9 oz
18 oz
11.2 lb
100ppm
2.4 oz
6 oz
12 oz
1.5 lb
15 lb

1 cup = 8 oz = 16 T
1T = .5 oz = 3 tsp
1 tsp = .167 oz

Note: Excessive hardness (higher than 230 ppm) sometimes found in well water situations, can be reduced by adding tap water, rain water, distilled water, or RO water. Water can also be softened by filtering it through peat or by adding acids.

Adjusting the pH in your Pond
Once your KH is in the ideal range, follow test kit directions to determine your pH. Test in the early morning and in the late afternoon, using a fresh sample of pond water. If the pH is between 6.8 - 8.2 and swings less than .8 during the day, all is good. If the pH swings more than .8 during the day, increase your buffering capacity (KH). If the pH is higher than 8.2 and KH is at or above
125 ppm, decrease pH with a safe acid compound. If the pH is lower than 6.8, simply change 20-25% of the water (our tap water tends to have a high pH).


Criteria for usage:
If buffering capacity (KH) is within the optimal range and the pH is more than 8.2, treat with sodium bisulfate or other acid.


Ideal pH range = 6.8 - 8.2, with a fluctuation of no more than 0.8 per day

To lower pH, add sodium bisulfate. Continue to test in the morning and evening. Treat once a day until the ideal range has been achieved.

To minimize stress to fish, do not lower more than 0.2 pH points per day.

 

Application Rates for Sodium Bisulfate
to lower pH

Conversions for Sodium Bisulfate

Pond size
100 gal 
250 gal 
500 gal
1000 gal
10,000 gal
With Fish
.15 oz
.38 oz
.75 oz
1.5 oz 
15 oz
Without Fish
.75 oz
1.9 oz
3.75 oz
7.5 oz
75 oz
1 cup = 12 oz = 16 T
1T = .75 oz = 3 tsp
1 tsp = .25 oz

 

 

 

 


Application Rates for Vinegar
(5% citric acid)
Application Rates for 20% Muriatic Acid
Pond size
10 gal
100 gal
1,000 gal
With Fish
2T
1.25 cup
12.50 cup
Without Fish
10T
6.25 cup
4 gal
Pond size
100 gal
1,000 gal
10,000 gal
With Fish
1 ml
10 ml = 2 tsp
.4 cup
Without Fish
5 ml = 1 tsp
50 ml = 10 tsp
2 cups

Be aware that vinegar may cause a bacterial bloom and cloud the water.

Note: Use of above acids will reduce KH.
2.4 oz Sodium Bisulfate/1000 gal will reduce KH by 10 ppm.

Putting it all together
First, start by referring to the simple planting and stocking guidelines provided in "Balancing the Water Garden". The idea is to have lots of plants to shade and compete with algae, fish (not too many though...and easy on the food, please!), and beneficial bacteria to consume organic debris.
Put it together in this order:

1. Dechlorinate the water
2. Test & Adjust the KH and pH
3. Add Plants
4. Add Beneficial Bacteria
5. Add Fish

Establishing a good balance in your pond is an interesting biological puzzle. Because new water will be added to the pond and beneficial bacteria action uses up carbonates, we recommend monthly re-testing of KH and pH throughout the growing season.

 

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