Raising alk with baking soda

[Saltfun2003]

My alk is currently at 6.4 want to raise it to about 9. Using this calculator http://reef.diesyst.com/cf/chemcalccf.html it says i need 20.3 tsp to raise it up. Does this seem about right total water volume is around 300g. How should i go about adding the baking soda? I was thinking about adding to to my ro topoff which is 20gal tank then mixing in the baking soda the 20g of ro water is gone in about 5 days. Would this be slow enough or should i do it in two batchs?

[bertoni]

That amount sounds reasonable, but I'd try using two doses unless I was very sure of the actual water volume. Just dissolve in some RO/DI water, as much as it takes. Adding via topoff water is fine if the dose gets added within 24 hours or so. Alkalinity can drop 2 dKH in a day fairly easily.