Auto Water Change Idea

So I have been rattling this idea around in my head for a while now and think I have a good base but just want to put it out there and see if I am missing anything.  The plan is to use 2 BRS Top-Off Dosers(50ml/min) mounted in the stand.  One will pull water from the sump down to the basement into a floor drain.  The second will pull water from a salt water reservoir in the basement up into the sump.  These pumps would run at the same time and run via my AC3.  There will be 2 float switches to override the system.  One will be in the sump to shut things down if water level gets to high(failure of pump taking water from sump to drain) and the second will be mounted in salt-water reservoir and mounted to shut things down when the saltwater level is too low.  Another failsafe would be mounting the line for the removal pump just below the water level so it would never remove too much water.
I have read other people doing this and said if you have them running simultaneously it should not affect my top-off sensor as the fluctuation will not be great enough.  My biggest concern is pumping the saltwater from the basement.  BRS states they have 20ft of max head and I do not think I would exceed 10 ft vertically but I will be running it 10-12ft horizontally.  I am not sure if they still remain accurate when you start pumping this far.   I do not want the waste pump going full blown 50 ml/min and the fresh saltwater pump only doing half of that.
Let me know what your thoughts.  I know some people will say keep it simple but if I can do this and eliminate any risks it would be nice for me while I am busy during the summer months.  With the failsafes the worst thing that could happen is my tank will not get an auto water change until I check on the system and figure out the problem(either failed waste pump or no saltwater in the reservoir)

 

They will run at a set amount of time. I have a similar setup running an auto water change on a freshwater tank but on that I have a pump(BRS 50ml/min Top-off pump) feeding fresh water to the tank and a drilled hole in the sump running to drain. So when the water level increases due to the new water the excess drains out. I had it running 7 hours a days at 7 different intervals but that proved too much constant run on the pump so I broke it down to 15 minute run times. Pretty sure when I calculated it at 7 hours run time per day that it equaled between 7 and 8 gallons.

 

Ya I will try e-mailing BRS and see what they have to say about head pressure on these little pumps. The reason for running the dosers is because of the accuracy which might go out the door if the head pressure fluctuates. At the same time I am not sure if there would be that much of an affect on the pump as it will just be pulling from that distant not pushing. Not sure if that makes sense but I will look into the idea before I run with it.