Raise alkalinity by adding a measured amount of baking soda, soda ash or a reef alkalinity product, split so it rises no more than about 1 dKH a day. To lift 100 L by 1 dKH you need about 3.0 g of baking soda. Dissolve it in RODI water, add it slowly into a high-flow area, and test again the next day before adding more.
Step 1: Confirm the reading
Before you add anything, make sure the low reading is real. Retest, check the kit’s expiry date, and if you can, compare with a second kit. Our guide to test kit mistakes covers the usual culprits.
Check calcium and magnesium at the same time. Raising alkalinity when calcium is also high makes precipitation more likely.
Step 2: Work out how much
You need your real water volume, your current reading and your target. The alkalinity dosing calculator does the sums and splits the total into daily steps.
| Additive | Amount | Effect on pH |
|---|---|---|
| Baking soda (sodium bicarbonate) | About 3.0 g | Lowers it slightly |
| Soda ash (sodium carbonate) | About 1.9 g | Raises it |
Scale in proportion: 200 L by 1.5 dKH needs about 9.0 g of baking soda. Bulk Reef Supply notes the pH difference between the two.
Step 3: Add it slowly
Weigh it on scales, dissolve it fully in RODI water and pour it slowly into the sump or another high-flow area, away from corals. Bulk Reef Supply suggests no more than 1.4 dKH a day and watching that pH doesn’t move more than 0.2. Our calculator defaults to 1 dKH a day to give you a margin.
For a liquid product, follow its label dose. Many two-part products are designed to be dosed alongside a calcium part, so check which one raises alkalinity.
Step 4: Test, then switch to maintenance
Test the next morning, at the same time you tested before. If it rose roughly as expected, add the next step. If not, check your volume figure before adding more.
Once you reach your target, the job changes. Work out how much your tank uses each day with the alkalinity consumption calculator, then replace that amount daily. A one-off correction without a daily dose will just fall again.
What not to do
Don’t correct a big shortfall in one go. Don’t use baking powder, which contains other ingredients. And don’t chase a number from someone else’s tank: a steady 8 dKH is better than a bouncing 9. See what alkalinity should be for choosing a target.
Common questions
How fast can I raise alkalinity?
Bulk Reef Supply suggests no more than 1.4 dKH a day. About 1 dKH a day is a cautious pace.
Can I use supermarket bicarbonate of soda?
Plain sodium bicarbonate works. Check the label lists nothing else, and never use baking powder.
Will raising alkalinity raise pH?
Soda ash raises pH. Baking soda slightly lowers it. Both raise alkalinity.
Sources and limits
Last checked 12 October 2026. Ranges and doses here come from the published sources below and from the chemistry of each additive. They’re starting points for your own tank, not guarantees for any coral.
- Bulk Reef Supply: sodium bicarbonate dosing instructions
- Randy Holmes-Farley, Reefkeeping: Reef Aquarium Water Parameters
- Hanna Instruments: how to test for alkalinity
Keep going
Work out how much to add · Free Reef Companion · All calculators