Just to give more information:
Readings from one sensor is sometimes affected If i change conditions for another sensor.

All sensors are in separate containers with soil and water.
Look at below results. Measurements at 17:09 has been steady like this for 15min ish, but when I add more water to soil where sensor "1" is, reading for sensor "2" changes by 5%.

2015-02-06 17:09:35 UTC+1 [Device] 0 raw: 39369 44%
2015-02-06 17:09:35 UTC+1 [Device] 1 raw: 22117 10%
2015-02-06 17:09:35 UTC+1 [Device] 2 raw: 45483 52%
2015-02-06 17:09:35 UTC+1 [Device] 3 raw: 42362 48%


2015-02-06 17:18:50 UTC+1 [Device] 0 raw: 39705 44%
2015-02-06 17:18:50 UTC+1 [Device] 1 raw: 28727 22%
2015-02-06 17:18:50 UTC+1 [Device] 2 raw: 49548 57%
2015-02-06 17:18:50 UTC+1 [Device] 3 raw: 42506 48%

 

Maybe you could measure the voltages of the op amps to make see what is changing.
Input, output, voltage to sensor.

 

Maybe you could measure the voltages of the op amps to make see what is changing.
Input, output, voltage to sensor.

Hi thanks again. Seemed that the reference voltage for the ADC was changed a bit, so I used a function on the imp to adjust for this called hardware.voltage() . It seems to work now, but who knows