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How to Properly Manage KH?

Updated: Jul 24, 2021

Photograph of UFO Chalice from the author's tank

Corals require a stable KH in order to function well. It is one of the most important parameters in a reef tank. Ask an owner of a thriving reef tank what her dKH (dKH is the unit of measure for KH) is at and chances are she will give you a definite number.

Managing KH is simple. Here, I have it broken in two parts.


Choosing a suitable KH value

Most reefers keep their KH between 7 and 12 dKH. Some successful reefers keep theirs out of this range but they are the exception.

I like to keep mine at 7.7 dKH. Why 7.7? I use Red Sea Reef Salt. It’s one of the cheapest brands in SG @$70 for a 22kg Bucket (Jun 2021 price) from C328 aka Clementi Florist and Aquarium. It has a dKH of 7.7 at 1.025 salinity. This means when I do a water change, my KH remains stable. And if my water parameters are off, water changes will bring me towards 7.7.

It's okay to pick a different KH value from the salt mix. It just means the KH is gonna bump around slightly whenever a water change is made but for me, I do as much as I can for stable water parameters and hope my corals appreciate it.


Keeping KH stable

Stability was mentioned a couple times in the previous paragraphs, what does it mean to have stable KH and how do I do it?

Stable KH means whenever a test is done for KH, the value stays the same week after week after week. In a freshly set up tank, the KH is usually stable for about 2-3 weeks. By the 3rd week, KH starts to fall and this is when the reefer needs to have some items ready and take action to keep KH stable.

What's needed?

The List

1. KH Test Kit (I use Salifert from Oceania Reefz)

2. Baking Soda (I use Arm & Hammer from Cold Storage)

3. 5ml Syringe

4. Dedication

Here’s what I recommend.

-- Step 1 --

Mix 100grams of baking soda into 1 litre of water and start by dosing a very very small amount of KH solution into your tank once a day and preferably at a fixed time period. When I started, I dosed 1ml into my 400L tank at 7:30am every morning before heading off to work.

-- Step 2 --

Test KH and write that in your phone. Also important to do this at a fixed time of day. I do my tests every 2 weeks at about 3pm.

-- Step 3 --

Compare today’s KH from two weeks ago.

If KH has gone up, reduce the dosing amount. Eg from 1ml down to 0.5ml.

If KH remains the same, great! Stick with your dosing amount.

If KH drops, CONGRATULATIONS. Your reek tank is thriving. They need more of the stuff. Increase your dosing amount.

For the lazy (eg. this author).

Dedication can be replaced with a doser. I use a Kamoer Single Head Doser. Goodbye to “Damn! I forgot to dose this morning again!” ALSO! The doser can dose multiple times a day and that keeps KH even more stable and unmoving.

Here’s a neat trick you can do with a doser. Using one can help combat evaporation. Instead of mixing 100grams of baking soda into 1L of water, try mixing just 50grams into 1L and DOUBLING the daily dosing amount. The extra water that goes into the tank replenishes water loss from evaporation.

The Author

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