Please help us our pond pH is 8.9, and we do not know why. All the fish seem to be doing fine, but even a large water change will only bring it down for a short time. Then for no reason, it goes right back up again to 8.9. Can you tell us why?

Q:

Please help us our pond pH is 8.9, and we do not know why. All the fish seem to be doing fine, but even a large water change will only bring it down for a short time. Then for no reason, it goes right back up again to 8.9. Can you tell us why?

 

A:

This question about high pH1 is asked more by pond hobbyists than one would like to imagine. pH is a negative-base ten logarithm of the effective hydrogen ion concentration in gram equivalents per liter. Various substances exhibit similar characteristics are how they react with others substances. A broad range of these characteristics have been divided into the two categories, acids and base, with the pH measurement is related to a ratio of the base components to acid components. 

What this means is, a substance that has one acid component for each-based component, is therefore neutral and has a pH value no greater than 7.0. Anything greater than 7.0 is considered to be less acids with more bass, otherwise known to be alkaline in nature with more dissolved calcium, magnesium and other compounds in the water; the “harder” the water the more alkaline it will become. Lime leaching out from concrete cinderblocks (which is one way to increase a falling pH in your pond) is a primary source of alkalinity; it can also increase by evaporation, which concentrates the source compounds in the water. Alkalinity2 is therefore naturally decreased over time through bacteria decomposition, which produces acid compounds that combined with and reduce the alkalinity compounds. 

You would not believe how many soi-disant experts instruct hobbyists to place cinderblocks in their ponds to lift up plants and/or to use them in building their pond filters. This also includes any blocks for paving or garden use made out of concrete. You will also find hobbyists that place flagstones or limestone around the perimeter of their ponds that also can elevate alkalinity levels after a hard rain. To test to see if your flagstones have a large quantity of calcium material in them is to place one gtt 3 (drop) of hydrochloric acid on the flagstone. If it then foams up, you now know it to have high concentrations of calcareous material imbedded in the stone.  

The reason you may need to know this information is that in our freshwater ponds, fish and plants have a difficult time in exceptionally hard water. You can use this procedure for any stones, rocks, and pebbles that you may wish to use in or near the perimeter of your pond. Consequently, any calcareous material will, for an undisclosed time, add hardness to our pond waters, but this may take years to dissipate. 

Consequently, anything that is greater than 7.0 is less acid and more base and anything less than 7.0 is more acid with less base. When acid like substances merged with base like substances, they react with each other producing some byproducts and leaving the resulting solution with a pH somewhere between the two original values. The further apart the pH of the two substances, the more energy is released in the reaction. 

 To minimize the initial pretreatment or curing of all new concrete items. Place the concrete item in a large container to adequate completely submerge it. Fill the container with water and add Muriatic acid (swimming pool acid) as required to adjust the pH to 5.0 levels. This will make the water in the container very acidic in nature. Make sure you circulate continuously and test daily, adding additional Muriatic acid to maintain the pH level until no additional acid is required. This normally takes two to three days. After the pretreatment, the curing process is complete and the concrete item is ready to be used. Properly treated concrete items will usually reach an equilibrium state where the production of compounds, which reduced the alkalinity, is matched by the components being leached out of the concrete. 

A word of warning: Only under extreme conditions should any chemical means be used to adjust the pH of a pond. Attempting to lower or raise the pH by chemical means can be particularly hazardous to all the inhabitants of the pond (especially if ammonia is present) and your biological filter is not up to handling to excessive ammonia. If your pH is reasonably stable and is somewhere between 6.5 and 8.5, not only is there no need to attempt to adjust it, but you probably will do more damage to the animals and biological filter by trying to change it. Therefore, you are better off leaving it alone.

 

1: pH is always written in lower case p, capital H. The “p” stands for power and the “H” is the chemical symbol of hydrogen. In equation form pH = -log (H+). The pH also affects the rate at which the nitrifying bacteria oxidize ammonia and nitrite because these bacteria have a preference pH range of 7.6 to 8.2. 

2: Alkalinity and hardness (a measure of the calcium and magnesium content) are not at all related. The confusion between the two is because of the use of the archaic European term “carbonate hardness,” mainly in discussions about reef tanks. Carbonate hardness is the same as alkalinity, neither of which is related to the amount of calcium and magnesium in the water. 

3: One drop-or exactly 0.05 milliliters. It is derived from the Latin gutta, which means, “Drop.” It is used more in the scientific and pharmaceutical circles and is an abbreviation.