PH can be effectively tested in runoff but it makes sense that ppm would be diluted depending on the amount of water. As someone else mentioned there are lots of other variables also. But you can get a general idea for comparison by using a fixed amount of water and a fixed soil sample size.
I use 100ml water (160 ppm in my case) and add 25ml soil sample. Stir and test the ppm immediately, after 1 minute and after 10 minutes. Of course super soil will be much higher than the base soil . I tested Roots Organic at 415 ppm - 470 ppm - 533 ppm (.5 meter)
Peat has very little nutrient value, is acidic as it breaks down, needs a wetting agent and of course perlite, pumice or diatomaceous earth for drainage. So once you have those areas of adding peat covered then consider the huge difference between the peat soil mix and Roots Organic. The Roots Organic has EWC, fertilizer, humates, kelp, rock dust etc. In order to be water only you would have to take the difference between the base soils into account. Good luck!