labstud4

I am producing lentiviruses using HEK 293T cells, and 24h post-transfection (Lipo2000 and OPTI-MEM) with my gene of interest, VSVg, and CMV helper plasmids, my cells appear to be contaminated. Under a microscope, I can see tiny black dots in the space surrounding the cells that do not float and are seemingly attached to the plate. The media remains clear. At 48h post-transfection, the black dots seem to have grown in number, yet the media still remains clear. After harvesting the viral supernatant, I will filter using 0.2um and then aliquot for infection. Does anybody know where this contamination comes from? Is this contamination--could these dots be granules secreted by the cells due to the stress caused by transfection?

I'm trying to make 0.5 L of 0.5M Tris, pH 8.0, and after calculations using the H-H equation, I found that 30.25 g of Tris (FW 121.14) into 400 mL of water, then add 22 mL of HCl (37% stock, 12 M), then fill with water up to 500 mL, and the pH should come out to 8.0. When I did that, the pH immediately dropped to ~ 3. After preparing another solution and slowly adding HCl, I found that ~ 14 mL of HCl would bring the pH down to 8.0. Can anybody tell me why this happened?