The pH and water hardness make a great deal of difference in the health of the plants growing above the fish that are in your aquarium. In a recent blog, the Aquaponics Source discussed the importance of pH and water hardness. In their post pH and Water Hardness in Your Aquaponics System Their overview comments on pH:
Most of us aquapons know that the health of all the creatures in our systems (fish, plants, worms, and bacteria) depends on proper pH. We also know that we are targeting pH in the 6.8 to 7.0 range but that we don’t have to worry about adjusting it until it goes down to 6.4 or up to 7.8. We also know that the best way to lower pH is with an acid, and that the best way to raise it is with carbonates or hydroxides. We know that rapid changes in pH can be very stressful to fish. And we know that the pH will probably decrease over time because the nitrogen cycle produces an acid (nitric).
They go on to discuss the other main consideration, hardness. It is the interaction between pH and water hardness that has caused so much frustration for aquarists and now people who are dealing with the water in an aquaponic system as well. The main point to consider, when dealing with a home aquarium/aquaponic filter system is that the pH should be kept between 6.8 and 7.0. For the aquarist this is a pretty common range and should be possible. The main problem is that the water often will come out much higher, 7.3 – 8.0 is quite common, at least for most of the places I have lived, so some adjustment may be required in both the pH and water hardness to make it suitable for the plants as well as the fish.
Hardness acts as a buffer to pH, it is a wall that must be overcome before any adjustment can be accomplished. It is much like inertia where the pH tends to remain the same until the buffering capacity is overcome, then what typically happens is the pH will move rapidly and much further than required. The most frustrating part is that it will often return to the original place within a twenty four hour period as the buffers re-establish themselves.
Test pH and Water Hardness after the Aquarium has Matured
You should measure the pH and KH (carbonate hardness) on a regular basis. I would not suggest any action be taken before your system is fully cycled. Once cycled, identify your baseline for pH and water hardness and at that point adjustment can be initiated. Don’t ever be too eager to get it fixed immediately. As mentioned, hardness is a blocker and absorbs acids to keep the pH constant. It may take a few days of slow and careful addition before the pH starts to move. You don’t want it move too quickly. Once the pH is at the proper level, test again in a day to ensure the buffer has been adjusted to the right level, chances are the pH will rise again if it has been pushed down.
Always remember the aquarium is a living system, and it generates acid as it breaks down the wastes. As time goes by, the water will tend to move more to the acid range. Water replacements often counteract that, but you may need to add alkalinity to keep it at the magic 6.8. As before, always make any moves to change pH slow and steady, rather than trying to move it all at once. The chemistry of pH and water hardness is not too tough, but the unseen buffers often make this a challenge to keep the 6.8 level all the time.
Aquaponics systems often use large amounts of water and require industrial strength adjustment. In the case of the aquarist, the amount of water is much less. There are quite a number of pH and water hardness adjustments that are safe for both plants and fish.