To create a Custom Substance from the Main Page, click Substance Selection, then in new window click "Add Custom"
Once the new window opens, you can type in the name you want to give it, the formula if you want it to be displayed, but when inputting liquid nutrients, you need to check the field next to Liquid. Doing so makes the Density field appear and this is where you would input the result of dividing the weight of the volume of nutirnet by the weight of the same volume of RODI. The result is the density. Usually 1 or 1.1, something like that. It is also important for some reason that the Purity be set to 100. It's likely that Purity means something else, but I didn't learn that yet.
Also, when creating custom substances, both wet or dry, you will need to reference the Guaranteed Analyses (GA) listed on the product label. The GA will tell you in percentages how much of each element is contained. Some things have micros, some don't. P and K, are usually listed as either P2O5, or K20 and you'll want to select each accordingly in their drop down menus. Silica also has a drop down that will be used the same way as Silica is delivered using K and will influence the final values. P and K, undergo a conversion factor which multiplies each by a known decimal to derive at available P and available K in the final recipe, otherwise the app will assume that other sources of each were used and will not be immediately available and will greatly affect the Result.
Edit - As a reference point, I'll include a screenshot of GH Flora Micro. Please note that the K has already been converted from K2O.
