I sympathize on doing test runs with plain water; Just used an in-line fertilizer injector with my garden hose to feed plants & was high & it was dark…pretty sure I got it right 
we’ll see.
Must say though… those black surfaces are not good, especially the nutrient reservoir. In winter yes, but not now. It’ll grow shit & the temp will possibly cause level fluctuations(?)…want root zone to be cool.
