Problem Maxi Doser reliability

[Laith_61]

I have a concern over the reliability of the Maxi Doser 2.2 to dose consistently accurate amounts.

I recently purchased the Maxi Doser to replace my Spectrapure system for AWCs. I programmed it to remove and add simultaneously 20 liters of waters a day. This is split into it running eight times a night every hour starting at midnight (2,500ml each time).

As the doser is new, I decided to calibrate frequently, thinking that the pumps need "breaking in" to run reliably. I ran three calibrations in a row on each pump and then took the average of the three. The figures below are these averages (ml/minute):

27/10 - Drain Pump: 256ml, Fill Pump: 329ml.
2/11 - Drain Pump: 242ml, Fill Pump: 328ml.
10/11 - Drain Pump: 255ml, Fill Pump: 251ml.
17/11 - Drain Pump: 245ml, Fill Pump: 310ml.
30/11 - Drain Pump: 254ml, Fill Pump: 246ml.
8/12 - Drain Pump: 248ml, Fill Pump: 322ml.
15/12 - Drain Pump: 253ml, Fill Pump: 258ml.

The drain pump pumps horizontally about 6 meters to a drain. The fill pump pumps from a saltwater reservoir that is right next to my sump, a distance of about 30-40cm.

The drain pump numbers are acceptable and what I would expect. However the fill pump numbers are not: they vary from 329ml/min to 246ml/min. This is a difference of 83ml/minute.

When changing 20 liters of water a day, this difference can quickly add up and start changing the salinity of the tank.

Do I have a defective pump? Is there anything I can do to make this pump more reliable?

Thanks!

Laith

[Laith_61]

Just to add that both pump are set to speed 3 (max).

And I have the doser sitting on it's end so the tubes run out to the left. Not sure whether this would have an impact, especially since the drain pump calibration is fine...

[Laith_61]

Any ideas?