Bottom Lines of pH in an Aquaponic System

imagesThe experts vary in defining the “perfect” pH in an aquaponics system. Murray Hallam of Australia, places it lower than most, from 6.2 to 6.4. He feels it is the best pH for fish, while  still in the ballpark for microorganisms. Most other experts prefer a higher pH in order to focus on the bread winners, the plants. One such aquaponics expert I like to quote is Dr. Wilson Lennard. His mark to reach in pH is 7.0 to 7.2.

Distilled, Rain water or water made from a reverse osmosis method will not have any dissolved salts carrying ions in your tank. But if you are starting with tap water, well water or water from a lake or pond, there will be mineral salts dissolved. In these waters you will have some dissolved minerals that effect your waters pH quite a bit. This is called “hardness”.  There are bits of information we all need to know about hardness. There are two types of hardness. The first type is carbonate hardness, referred to as KH, alkalinity of BUFFERING CAPACITY. The second type of hardness is called general hardness or simply GH. The GH refers to the concentration of calcium and magnesium ions in the water.

It is the buffering capacity, KH that effects pH factor more. The buffering capacity acts like sponge soaking up acids or bases is in your tank or is added to your system. The newly added ions will not effect your waters pH until that sponge (the KH0 is saturated and full. Add all the acids or basses you like but the pH wont budge. Burt when it does reach it’s limit, a very small addition of base/acid will start effecting your levels. That is why many times you can add a bit of acid (for example) and the pH doesn’t budge. You do it again and again with the same results. Then all of a sudden you add one more drop and the numbers fall off the cliff.  So the best way to imagine what happened is that you ‘filled up’ the sponge.

KH levels are measurable. Knowing your KH will help you manage your pH. The larger the KH number, the more resistant your tank water will be to a pH change. You can measure your KH if you have a KH meter.  They give readings in dH (degree hardness) Having a higher KH level can be beneficial in a fully cycled system. This is because the nitrification process’s byproduct is nitric acid. This steadily produced nitric acid steadily drives your pH down into acid ranges, in an unbuffered environment. A rule of thumb is that a KH of less than 4.5 dH means that you don’t have much buffering capacity and you should be checking your pH a lot more often.

You can increase your system’s buffering capacity by add calcium and/or potassium carbonate, a little at a time. Over time, you will build an solid buffer and your system will become more and more pH stable.