Why are algae a problem?
Algae belong in the pond as much as other water organisms. You can’t prevent their occurrence, at least not without a lot of effort. As long as the algae growth remains low or it doesn’t noticeably gain the upper hand there is no need to worry.
Strong algae growth, however, has a dramatic effect on the water: Algae are plants and produce oxygen during the day (which is positive). But at night the situation reverses and the algae consume oxygen. With a heavy algae infestation the oxygen can drop into dangerous ranges at night and threaten the life in the garden pond. It is then advisable to aerate at night.
Exposed to light (i.e. during the day), the algae continue to consume carbon dioxide (CO2) like the water plants. This consumption can lead to an extreme increase in the pH level (acidity > 9), which in turn leads to a life-threatening environment. During the night they produce carbon dioxide again (just like the other plants), and this decreases the pH level.
If the CO2 content in the water is no longer sufficient, algae are able to dissolve the CO2 out of the carbonate hardness (KH). The result is a decrease of this important water parameter which leads to an unstable pH level. Now the pH level drops at night (mostly to values up to about 6) and rise during the day to far too high values (up to values over 10), and this can mean serious problems for all living organisms in the pond.
Note: A change of one step in the pH value means a tenfold of the lye amount (pH value increases) or the acid amount (pH value decreases). A change of two steps is a hundredfold change of concentration, 3 steps imply a thousandfold change of concentration.
Finally it is worth mentioning that dying algae are broken down by bacteria during oxygen consumption. Therefore the water needs to be aerated additionally when algae die, either by themselves or when combated actively.
These processes seem to be very complicated at first glance. But don’t worry: If you approach them step by step and break them down into single processes, they are not difficult to understand and easy to handle – we promise!