Using sodium bicarb to increase alk

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Go slow, there is no rush, it is easy to overshoot and if your alk goes to high you will have CaCO3 precipitating out as a snowstorm.

In addition, I would consider your pH and decide whether to use sodium bicarb or else baked sodium bicarb. If the pH is high (unlikely with low alk) then use sodium bicarb, if it is on the low side you might want to use baked sodium bicarb or a mixture of the two.

Just a couple days ago I tried to correct my low alk, overshot and now my alk is off the scale on my Salifert test kit, no ill effects on the tank but this is just a reminder to do small increments and test before each addition.