Introduction

Carbonates are important compounds in the reef aquarium as it is the building block in the formation of the skeletons and shells for many organisms. However carbonates are difficult to test for directly, so we measure carbonates indirectly using an alkalinity test. This test measures how much acid is required to lower the pH of the solution down to the 4-5 range. Alkalinity in a reef aquarium should be maintained between 7 to 11 dKH.

For further information click on these links:
http://www.advancedaquarist.com/issues/feb2002/chemistry.htm
http://ozreef.org/library/articles/alkalinity.html
http://reefkeeping.com/issues/2002-04/rhf/feature/index.php
http://www.advancedaquarist.com/issues/nov2002/chem.htm

You should check the magnesium and calcium levels and make any adjustments to those before adjusting the alkalinity level.

Increasing your alkalinity level in your tank is fairly easy and can be done by using an Sodium Bicarbonate - NaHCO₃ (Baking soda/Bicarbonate of soda - can be bought in supermarkets). It is important not to buy Baking Powder which is different and has phosphate as the main ingredient.

Using baking soda (sodium bicarbonate) can cause the temporary drop in the pH of the tank. You can stop this by baking the baking soda in the oven, this converts the sodium bicarbonate into sodium carbonate. To do this spread the baking soda on a tray and bake for 1 hour in the oven at 200° (400°F).

If your alkalinity levels are high, then test a fresh salt mix to see what the alkalinity levels are, if unusually high then consider changing your salt brand. Carrying out regular water changes with a salt containing less alkalinity than your tank level, will gradually bring the alkalinity levels down. However carbonates are generally consumed in the tank over time by corals, algae etc. So unless the level is very high, it is normally best to carry on with your normal water change routine and wait for the alkalinity level to drop.

Application

Using the calculator below find out the dosage amount. Weigh the dosage carefully.

Mix the dose with 1/2 to 1 litre of RO water. Stir thoroughly to dissolve the salts until the mixture is clear. Then drip the mixture slowly over the course of several hours into a high flow area of the tank such as weir, sump return area etc.

Due to the sensitivity of marine organisms, it is not advisable to raise alkalinity by more than 1 dKH (0.36 meq/l) per day.

When increasing alkalinity, it is not advisable to perform other supplements at the same time. As this could cause chemical reactions in the aquarium and the desired increase will not be obtained.

If you are unsure about anything discussed above, raise a thread in the 'Help and advise' or 'Chemistry' areas of the forum.