The phthalates in PVC have minor to no dissolving tendency  into pool water. Maybe you have to worry more of the chemicals from the paint.

Don't think I have ever worked with the Benedict's reagent, but in general I see nothing wrong with your samples. Seems like the amount of precipitate is higher for the samples with higher amount of glucose, which is what is expected. Colors that appear during the procedure are probably intermittent - as the precipitate ages (it can need just minutes to do so in general, no idea about this specific case) particles of the precipitate grow on average (more precisely: smaller ones disappear, larger ones get larger) and settle down, leaving just the blue solution.

You should find this link useful: https://www.chemguide.co.uk/analysis/masspec/howitworks.html#top

Also if you are studying UK A-level chemistry I would encourage you to explore the chemguide site. It is pitched at UK A-level and is very extensive in its subject matter. It is also reliable in its information.

Silveracetate would work. The others all more or less not soluble in water.You could try to dissolve silveroxide in nitric acid to produce silver nitrate.  The halogenids can be dissolved in ammonia or Thiosulfate.

I had a practical exam today, which I create solutions of glucose with different concentrations (0%, 0.25%, 0.5%, 1%, 1.5% and 2%), put Benedict's reagent, and observe the color change. In each test tube, I added 1 mL of the solution and 2 mL of the Benedict reagent, total of 3 mL. And then I heated the test tube in a water bath at 50-60 deg C until I observe a color change. The result is attached, where the top one is 2%, 1.5%, 1%, 0.5%, 0.25%, and 0% (very bottom). I expected a color change from blue to red (green, yellow, orange) for each glucose solution, however only red precipitate that appears in my test tube. Besides that, my peers' result showed the expected result (the color gradient). What could be the error behind my result? Thank you.