Help with 2.1 doser head

[Potatohead]

I've had a four head 2.1 (stand alone) doser since March. I've been having a problem with the second head siphoning backwards. If I leave it long enough (a full day) it will completely siphon back through the pump into the dosing container. I thought it was air getting into the lines at the pump but I have redone it like three times and it seems to me then the liquid would flow away from the pump in that case. I have also taken the tube/rollers out and reassembled it all to double check that as well.

Any ideas? The other three pumps are all fine. The only other difference is the one that siphons back runs at a different speed than the other three but I can't see that being an issue.

Thanks

 

[reefwiser]

Have you posted on the GHL forum
Could be a bad roller assembly causing the issue.

 

[Potatohead]

No I just tried here.

Thanks

 

[StAiden]

I have a similar issue and was told that sometimes the rollers will stop in a position that is not entirely pinching the tube. Try raising the dosing container so it doesn't create a Venturi. See if you can put it level with the end of the tube that is in your tank or sump.