I think white is an indication for infection, but GIGO (garbage in garbage out ... just an eg, not that your food quality is poor ).

I suspect that your previous food has lots of red coloring (maybe red pigments for color enhancements), but your current food has lots of green matter, which I think should be normal.

BTY, I believe that your fish should remain healthy without feeding for 3-4 days. I rather not feed them and ensure good water quality, rather than feeding and having the chance of poor water quality!!!

Never used those blocks, but I assume they are safe.