This morning’s test results were:
- KH: 10 ° (179.0 ppm)
- ammonia: 2-3 ppm
- nitrite: 0.5 ppm
- nitrate: 5 ppm
So the KH really is dropping, and I have now remembered that the reason it rose was not the sand, but that I used tap water to top up! Nitrite and nitrate are definitely rising.