JBL PondCheck pH and KH test for ponds, drop-based

For pH, the colour obtained is compared with the colour chart, against a white background, after waiting 5 minutes. The pH of a balanced pond sits between 7.5 in the morning and 8.5 in the evening, because pH naturally rises during the day: plants and algae consume the dissolved carbon dioxide during photosynthesis. So always measure at the same time, preferably in the morning, to compare your readings from one week to the next. For KH, the reading is even simpler: the water turns blue when the buffer is sufficient, and orange-yellow when it is too low. In the latter case, your water no longer cushions variations, and the pH can drop sharply overnight.

In an aquaponic system, the filter bacteria convert the ammonia excreted by the fish into nitrite, then into nitrate. This nitrification releases acidity, which the carbonates neutralise as they are used up. The KH reserve therefore falls continuously, all the faster when the tank is heavily stocked and fed. When it runs out, the pH drops in turn, the filter bacteria slow down and ammonia builds up. A check once a week tells you when to top up the reserve, before nitrification slows down. Plants also absorb iron and phosphorus less well when the pH rises, as the article on pH regulation in aquaponics explains: in aquaponics, the target is therefore a little lower than in an ornamental pond, between 6.4 and 7.5.