Rain – A problem for fish and good for algae

In the garden pond the pH rises to over 10 if the carbonate hardness is insufficient or non-existent. In unbuffered ponds the pH level can even fluctuate up to 4 pH value levels within one day. This happens all the more on summer days (with a lot of sunshine), during algae blooms and after heavy rainfalls.

This is very dangerous for your fish. pH values over 9 can cause acid burns on the skin and gills. The first signs are a whitish skin clouding and fringes of the fins, and sometimes even respiratory distress. Because it also affects filter bacteria, this can, in the worst case, also result in ammonia poisoning.

Therefore, make sure the carbonate hardness is always kept over 4 °dKH and the pH value between 7.5 and 8.5.

Why do the carbonate hardness and the general hardness disappear? You will find some examples here:

  • Heavy rainfall; rain is hardness-free (soft) water and leads to a dilution effect of the minerals. Biogenic decalcification; in case of a carbon dioxide deficiency in the water some plants, in particular algae, are able to cover the CO2 demand from the biogenic decalcification. Nitrification in the filter; nitrite is generated through the nitrification caused by filter bacteria and this consumes hydrogen carbonates. As a result the carbonate hardness decreases. Mineral consumption through plants, algae, insects, invertebrates and fish; all organisms need minerals for their own metabolism and growth, including calcium, magnesium and others.

The instability of the pH level weakens any competition and creates ideal growth conditions for the algae. This is why too low carbonate hardness can promote the algae. In addition rainfall inevitably leads to phosphates leaking into the pond from the garden soil (which is usually rich in nutrients). This only happens when the pond is built into the ground (not raised).

Test every 3 weeks with the JBL PondCheck the stability of the pond water. If this is not the case you can use JBL StabiloPond KH to return the missing minerals to the pond and re-establish the balance.

© 09.09.2015
Matthias Wiesensee
Matthias Wiesensee
M.Sc. Wirtschaftsinformatik
JBL GmbH & Co. KG

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