If tank water quickly drops in pH, its because acidification is coming from metabolism byproducts, and fish urine (uric acid) and not being buffered. Water changes dilute fish urine, and freshwater fish are constantly urinating.
The tube on the right appears to coincide with the water quality report pH (8ish) of the water leaving the purification plant.
If it was my tank, and I was looking at the difference in the pH in the test tubes between high pH tap water, and a much lower pH in the tank, I would consider doing more frequent water changes to maintain a more stable pH in the tank. This would also dilute those nitrates.
To me, the tank water dropped quite bit in pH over a short time (?) indicating the fish urine is overwhelming the buffering capacity of the water.
And from the alkalinity of the water tests done at the lab, the buffering capacity is quite good.
The tube on the right appears to coincide with the water quality report pH (8ish) of the water leaving the purification plant.
If it was my tank, and I was looking at the difference in the pH in the test tubes between high pH tap water, and a much lower pH in the tank, I would consider doing more frequent water changes to maintain a more stable pH in the tank. This would also dilute those nitrates.
To me, the tank water dropped quite bit in pH over a short time (?) indicating the fish urine is overwhelming the buffering capacity of the water.
And from the alkalinity of the water tests done at the lab, the buffering capacity is quite good.