John, no discernible effects;good or bad.
I agree don't dose without testing is a good general rule, imo.
Unfortunately , there are a number of things we can't test for with any reasonable expectation of accuracy with hobby grade equipment; for example: organic carbon( vodka, vinegar,sugar, polymer pellets, etc);K(potassium), iodine tests are weak and hard to read;copper tests don't go low enough, etc. Carefully calculated measures are often the best we can do Testing can be tedious and fraught with inaccuracy. Some folks over react to an inaccurate test result.
The quantity of K Potassium present in seawater is such that a calculated dose for a 25ppm bump shouldn't and didn't hurt anything. I was concerned that it might be low due to bacterial growth associated with organic carbon( in my case vodka/ vinegar dosing).
We all dose lot's of things we can't measure in our salt mix and major supplements too. The market takes advantage of the uncertainty with a plethora of products ( ammino acids,secret elixirs,reef safe medications, bacterial supplements,trace elements ,etc) without telling us what's in them or any real evidence that they are helpful.
So all in all it's hard to tell exactly what's in tank water but knowing as much as you can about it and monitoring those things you can diligently by test when possible or at least close observation for those you can't accurately test is important, imo.