18'+ Lift and Peristaltic Pump Not Limited by Head Pressure

[gsjmia]

I have wanted to auto dose for a while, but I have about a 5' lift from the floor to the top of the tank. I tried little Rio pumps and even big giant fountain pumps at HD but they couldn't lift 5'. I even tried to reduce the hose size down to about 1/16" for IV hose, thinking it could push-but I guess that old saying of running up against a "fundamental" came true.

This left peristaltic pumps. Long story short, I bought 2 Drew's Doser Pumps for $89 each at Bulk Reef supply. They look suspiciously a lot like other pumps, but they seemed cheaper, so I bought. Here are the contents of the box, pump, hose, measuring cup, instructions:
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It pumped the 5' with no problem, but I was curious about how far it would pump, having seen others post the same question. So I decided to do the following test:

I bought 20' of cheap hose:
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Here is the suction side (I cut suction hose from another hose--the 20' remained intact):
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Here is the assembled test set up:
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I filled the hose by siphon to get all the air out and then connected it to the pump.

I set the timer on my smart phone for 15 minutes and plugged it in. I chose 15 minutes thinking that the second test might take a while to build up pressure before it started pumping (it didn't) to give it time to get going.

Ground level control test begins--note that the pump is going through all 20' of hose (not shown), but the input and output are roughly the same (in hindsight, I should have held the cup to the top of the jug so it wouldn't get a siphon effect-not a big deal):
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[gsjmia]

CONTINUED:

After 15 min, it pulled the plug out and it had pumped a little less than 20ml. I marked the cup with a sharpie:
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Here is the 18' test setup:
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Here is a close up of the last 3':
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Set the timer on my phone for the same 15 minutes, plugged it in and it started to pump immediately with zero delay (the hose remained filled from the previous test-would have taken an hour or so to have the pump fill the hose without help):
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After 15 minutes I pulled the plug. Here is the result:
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Between the first and second test, there was a pencil line of difference between the two results which is insignificant. The difference may have been a result of timing differences which resulted in one extra stroke on the pump-or it may have been the 18' of head pressure-don't know and don't care because the difference is insignificant.

Drew's pump has 4 rollers and at least 2 rollers are always touching the hose, so no check valve is required. During the tall test and after the pump was turned off and the hose was still 18' high and filled with water, I pulled the hose off the suction side to see if it would back flow, but not a drop came out.

I don't think Drew's pump is anything special and any 4 roller pump should produce the same results. But it was the cheapest pump I could find at the time.

I am satisfied but still curious-I wonder how high it would pump before the head pressure limited the lift?