does Baking soda raise pH?

I am sorry but I don't see how baking soda comes in?

Yes it will raise your pH. And more importantly it will raise your kH which will keep your pH from dropping so much. You need to test pH at the same point in your light cycle in a planted tank. The pH can vary quite a bit, going up while the lights are on and the plants are absorbing CO2 and dropping at night when they release CO2. A tsp is about right in the 20, a bit more in the 29. Dissolve it in a cup of tank water before adding.

baking soda will raise your ph but its only temporary. you need to raise the kh to keep it up. a small bag of crushed coral in the tank or filter will help

Baking soda is chemically known as Sodium bicarbonate, which many "pH Uppers" are! In other words, yes. Add it very gradually and check pH often. If you pH is slipping, find the root cause.

http://www.aquarianow.com

you have another thread mentioning you might start diy co2. co2 lowers PH.

Why do you want to change your PH?? what is your end results you are trying to achieve? your ph doesnt have to be 7, fish can live in a very wide ph range.

It will not, however, change the amount that CO2 changes your pH during the day. It will change the range, but not the size of the range. Fortunately, pH changes do not, contrary to popular belief, in and of themselves bother the fish.

Measure KH. That is the important factor here.

And why are we in the process of raising the PH in the first place, if it is at 6.4 ?
Lets see some more details?
Location, KH, GH, what is in the tanks ...