Originally Posted by FragIt Dan (Post 735495)

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