I used to try those parasitic pumps and one day I while out at MAX on the west coast found a used [Pulsafeeder's Chem-Tech Series 100D motor driven diaphragm metering pump and it has been running for 15 years plus without ANY maint whatsoever, and noticed my levels dropping last week, also noted the pump sounded labored, well the motor finally quit, seems to have a winding gone as just fights to not turn while energized but turns free when off.]So what did I do, I found a new old stock one on ebay for $150 shipped. So glad I found another dual pump setup, and it's the exact same model so no changes needed. I bought mine used so to last 15 years plus is quite the testament for these industrial pumps. SO if your tired of your repairing your parasitic type doser I'd highly recommend these. I know they don't have any computers to drive them but my apex runs it just fine with the ability to adjust each channel they work great. And they can pump up like 20' with no head loss , no surprise since they are rated to 75psi .