Fertilizing without upsetting the reading
Why fertilizer skews the moisture reading — and how to do it right
Fertilizer and moisture measurement do not get along, and there is a physical reason: the sensor does not measure water, it measures how the soil behaves electrically. Water changes that a lot — but so do dissolved salts. Freshly fertilized soil therefore looks wetter to the sensor than it is.
The consequence is awkward: the device sees a high value and waters less. So the plant gets too little at exactly the moment it needs to wash the fertilizer in.
Mineral liquid feed is worst (it is pure salt in water); organic fertilizer far less, because soil organisms have to break it down first.
HydroCommander cannot correct for this — its sensor reports temperature and moisture, not conductivity. So the only remedy is doing it in the right order.
1In AI mode: switch on maintenance mode
In AI mode, switch on maintenance mode before you fertilize. It pauses every zone and freezes statistics and AI learning.
This is the step that matters: without it the AI learns from the salt jump — it memorizes "watering makes the value rise sharply" and permanently doses too sparingly afterwards. In Automatic and Schedule mode nothing is learned — maintenance mode is not needed there.
In the app
Settings → expand the "Maintenance" section → switch on maintenance mode.
On the device
Settings → maintenance mode.
See also: Maintenance mode
2Wait for the value to settle
After fertilizing, the sensor reads too high for a while. Depending on the substrate it takes a few hours to about a day for the salt to spread through the pot.
While the value is obviously too high (the soil feels dry on top but the display says 80%), that is not a sensor fault.
Tip
Look at the history: an upward jump that does not come back down is typical of fertilizer. A jump that recedes after a few hours was water.
3Switch maintenance mode off again
Once the value looks plausible again, switch maintenance mode off. From then on the zone counts normally again.
Caution
Do not forget — in maintenance mode no zone waters automatically.
4Rinse the sensor now and then
If you feed mineral fertilizer regularly, a white salt film builds up on the sensing area over time. It makes the sensor read permanently too wet.
Every few months: pull the sensor out, rinse it under clean water, dry it, put it back. Stubborn deposits come off with a little isopropyl alcohol.
Tip
No calibration is needed afterwards — the sensors are factory-calibrated. If a sensor still reads too wet after rinsing, there is still residue on the sensing area.
See also: Understanding & checking sensors
IN SHORT
- In AI mode: maintenance mode on
- Fertilize
- Wait until the value is plausible again
- Maintenance mode off
NEVER put fertilizer in the tank. It clogs pump, hoses and suction filter, and the drip points crust over.
Sensors count as consumables. Permanent contact with fertilizer salts shortens their life — rinsing is the most effective countermeasure.