Copper carbonate is blue-green and not very soluble in water (solubility product of 1.4x10^-10) so in a pool with 100 ppm TA, 30 ppm CYA and pH of 7.5, the carbonate is 3.9x10^-6 moles/liter so that means you can have up to 1.4x10^-10/3.9x10^-6 = 3.6x10^-5 moles/liter of copper which is 2.3 ppm.

So you are at the "edge" of precipitating copper carbonate and the addition of the baking soda created a locally high level of carbonate until it more fully dispersed. Basically, if your pool's pH rises, then you will very likely get the blue-green tint again. So I suggest using a metal sequestrant.

Another compound is copper hydroxide which is bluish. It's solubility product is 2.2x10^-20 (other sources say 4.8x10^-20) and the pool water as described above has hydroxide concentration of 5.3x10^-7 moles/liter so theoretically this is even more likely to precipitate, but in practice it looks like it doesn't (for reasons I do not know).

Richard