DIY Co2 or NutraFin Co2

adding baking soda buffers the mixture so that it doesn't run out that fast and also to control the bubbling rate it'll not affect your tank's kh. i personally think it's advisable to add so that the mixture wont go haywire(ie produce a lot of co2 in the first few days then after that the mixture just dies )
hmmm but when the water comes out from the sump it'll be gone since it's sort of like a waterfall(?) at the output area? since there's surface agitation the co2 will be gone... perhaps it's more advisable to have another powerhead at a more remote area in the tank where there's not that much surface agitation so as to prevent co2 loss