marine magic doser not working

[FragIt Dan]

Update to my post below... The channel running the over width tubing that the doser came with has stopped rotating/pumping, I suspect due to the increased resistance from the wider tubing. I would not use the wider tubing. I switched the heads to one that was working with the stock tubing and it began pumping again, so hopefully no damage was done,
Dan

Originally Posted by FragIt Dan

My pumps run for about 300 seconds on S4/day in a position approximately level with both chamber and hose outlet.

The tubing has been a nightmare to find, I have yet to find a source and am considering requesting a batch from Marine Magic to send out to people as needed.
What works (read warning below): use the original soft tubing that the pump comes with. I think this is supposed to be used to run a line from the head to the dosing chamber as it is 1/4" instead of 1/8"(?). Because it is wider than the tubing that runs through the head, you will need to get a standard air hose coupling (instead of the adapter that comes with the doser). This also removes the need to find those little, VERY fragile adapters.
WARNING: Because this solution expands the diameter of the tubing in the head, expect the head to pump a significantly greater volume, leaving you vulnerable to OVERDOSING your tank. Measure the new volume being dosed and adjust accordingly.
What DOESN'T work: I sourced some intravenous tubing from a medical supply place that appeared to be identicle to the stock tubing in the head. I couldn't get suction using this tubing despite thorough testing. Others may find a slightly different version that works which would be of interest to me. I have also broken a few of those little hose coupling adapters and can't find more, so using a standard size tubing solves that issue too.

I also have not wanted to try standard air tubing due to the stiffness. I suspect the additional stiffness would add substantial wear to the pump motor, if it would even work at all.
Dan