#2 You only need enough 'stuff' to be clearly visible. Use whatever pool acid you have -- either dry sodium bisulfate (pH Down) or muriatic acid. If you haven't used muriatic before, get some pH Down and use it. And yes, plain vitamin C tablets like people take.

#7 Your bucket test indicates that your fill water has little or no metal in it. That points the finger back at the copper in the Intex SWCG.