I use the Aquamedic 4 head dose pump. I use 2 heads per tank. 1 head doses from reservoir of KNO3 and KH2PO4 for macro dosing. My primary tank is a 55. I mix 1.75 tsp KNO3 and .5 tsp KH2PO4 per 3qts of water in macro reservoir. I installed a small powerhead in reservoir that runs on a timer that comes on 30 minutes prior to dosing event and runs 1 hour to insure proper mixing and consistency. Macro head cycles daily for 8 minutes and 20 seconds and consistently delivers 1 cup of solution to water column, keeping NO3 at 15-20ppm and PO4 at .5-1.0ppm without fail. I intend to move to a larger reservoir and further dillute solution so I can add slightly more volume to tank to compensate for evaporation. Second head doses micros. I pull undilluted Seachem Flourish (todays macro cycle just initiated as I'm typing, nice) from one reservoir and undilluted Seachem Iron from a second reservoir. I initially mixed Flourish and Fe dilluted with water in a bucket and in less than 2 weeks a nasty rust colored sludge was overtaking the bucket and clogging things up. The two micro reservoir pick ups are t'd together and mixed just a few inches from intake of pump. Each solution is metered through its own hydraulic flow control needle valve. The solution mixes very accurately at a ratio of 1.3 to 1.0 up to 1.7 to 1.0 with a goal mixing ratio of 1.43 to 1.0. I never see a dose stray in quantity by more than .5 grams. A deviation of more than .2 grams happens about 2 out of 5 cycles and is always to the positive side of dosing goal. This head cycles for 15 seconds daily.
All this being said I must say it was quite alot of work over a significant period of time to get this system right. Mostly because I designed and engineered everything other than the dose pump from scratch and there was alot of trial and error in learning what works and what does not and why. There was also a great deal of time and energy spent monitoring dosing to be sure cycles were consistent and accurate. I estimate I spent in time and energy the equivalent of 2+ years of daily dosing by hand to get the automated dosing functioning with precision and repeatability. I am now able to set these systems up in thier entirety in about 10 hours not counting fab time for reservoirs, racks, etc. There is then an additional daily monitoring of reservoir depletion and water column parameters of at least 1 week but ususally 2 weeks to have valves and cycles tuned in properly for the particular tank. Beyond all this there is the expense of components to be accounted for. When money is no problem I use Grundfos batch dosing pumps used in process systems to dose each fert. individually. These pumps are a dream. The accuracy of each batch reads out to .001 ml. They use VFD motors to operate a diaphragm pump. Simply enter dose qauntity for batch and trigger cycle events with pulse input from a seperate timer or other switch mechanism. These pumps cost $1100.00 to $1500.00 each.