Best dosing accuracy is achieved with larger dose sizes and if any of the ratios of a multi-part mix is set to a small value then it important to ensure that its dose time is still above 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. E.g. 1 part nutrient to 3 parts of water (makes a 25% solution). This would result in each dose casing the EC to rise by ¼ of its previous value.
Another approach is to dilute only the nutrient parts that require the low % ratios. 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.
Using a schedule
Using IntelliGrow, it is possible to schedule automatic changes in a two or three-part dosing regime. To do this go into “Configure” tab and select “two or three-part dosing” and “Scheduling”. A new tab “Scheduling” will appear which will allow you to tabulate the required Pt1:pt2:Pt3 ratios and EC for each stage of growth. Note that changes can be on a daily basis or less often as necessary. It is usually required to make frequent changes during the cutting or seedling stage and then less frequently as the crop matures.
Of course, every crop develops at a different rate and so the table is very easy to modify. Days can be added, or deleted at will and dates can easily be changed.
Changes will only happen if IntelliGrow is connected and on line. If the conroller is taken “off-line” then when it is next connected if any change is required it will be made straight away. Normally, changes will take place at midnight preceding the date specified.