Dose times and interval are set by trial and error with the best accuracy achieved with larger dose sizes. The smaller the reservoir the smaller the dose times need to be. The strength or concentration of your stock solutions will also affect the dose time setting. Obviously, the stronger the stock solution, the shorter the time the pump runs. If you are using a small reservoir tank you must ensure that your stock solutions are very dilute. Also, if you are using a multi-part mix, you need to ensure that the smallest value will have a dose time greater than 1 second.
Ideally, you are trying to achieve a dose time such that the EC(TDS) goes up by about 0.1EC (50 ppm) for each dose. If you need to set the dose time to a very small number to achieve this then you need to dilute the stock solution. The minimum time that any pump should run for is 1 second. For example, say a dose time is set to 5 seconds and one part is set to a ratio of 10%. This means that a ratio of 100% = 5 seconds and so a ratio of 10% will equal only ½ second. This is not sufficient time for a pump to run so the dosing of this part will be very inaccurate if it manages to dose at all. The solution is to increase the dose time to 10 or even better 20 seconds. At ten seconds the 10% component will dose for 1 second (just long enough but still not very accurate) while at 20 seconds it will dose for 2 seconds which should be much more accurate.
However, you may now find that each of these larger nutrient doses raises the EC by more than the desired 0.1 EC (50ppm). The only solution to this is either to 1) dilute the stock solutions, or 2) use a larger reservoir tank or even a combination of both. If diluting the stock solutions, it is important to dilute them all in exactly the same ratio. For example, a recipe recommends 100:50:10. If the dose size was set to 5 seconds the part A would dose for 5 seconds, part B for 2.5 and part C for only 1/2 second. By diluting part C in water with one part C to 4 parts water we will reduce its strength to 1/5th of the original. Then we would schedule 100:50:50 which would be much more accurate.
The process is similar for pH dosing where you are trying to achieve a change of, about, 0.1pH for each dose.
The dose interval is set to allow time for a dose to fully mix in before the controller makes the decision as to whether another dose is required. Normally set to 1 minute for a small tank and up to 10 minutes for very large systems.
If the dose interval is set to zero, then the valves will open continuously while the measured EC and pH are below the set point and close as soon as they exceed the setpoint. This feature can be used as a simple in-line injection system in which irrigation water is rapidly taken from a small tank and fresh water is added simultaneously such that rapid dosing is required to maintain the EC and pH.
When using water to reduce EC the water on time should be set so that each time it adds water it dilutes the nutrient by about 0.1EC (1CF or 500ppm).