I do have 1 matter of fact I got 3
First, I'd like to steer you away from the use of 'ppm', because it isn't just one scale; there are many of them. This creates obvious confusion, so my suggestion is to use EC, or electrical conductivity. It's what your meter actually reads anyway and can be converted to all the other scales.
That said, if your runoff water is any higher than EC 3.0, I'd recommend running a low strength nutrient solution through it in a large enough quantity to see 25-50% runoff. This will allow excess salts to be flushed out. Don't use water without nutrients for this purpose in coco, that will screw them up but good, lol