Sodium bicarbonate vs sodium carbonate

[Reef Pilot]

Any opinions and experience about which is better? In the past have used sodium carbonate (from Seachem), but in the last year have gone to the much cheaper bulk bicarbonate. My SPS growth has not been as fast lately (but there may have been other reasons).

I have not tested my pH for a long time,... maybe I should. Does higher (and consistent pH) make a difference to SPS? The carbonate is supposed to be better to maintain a higher pH.