Why Kalk is King in the Saltwater Tank Additive World


Of all the things you can add, dose, or supplement to your tank, the one that is king of them all is kalkwasser (a.k.a “kalk”).

Here’s why:

  1. It raises your Alkalinity/pH/calcium levels all at the same time
  2. It is super cheap

One of the best ways to have a reef tank that really shines is to keep all your levels as stable as possible. Kalk is great for this job as it keeps your Alk/pH/Ca levels stable. It mixes up to a pH around 12, so a small amount of it can raise your pH A LOT. So much so, that you have to make sure you don’t dose too much (I’ll talk about that tomorrow). The same thing applies with Alkalinity – a little bit of kalk can do wonders for your Alk. The more stable your pH and Alk, the happier your corals are.

And it adds lots of calcium to your tank so if you have clams/SPS/LPS, then you will have no problem maintaining your calcium levels.

Kalk takes care of all these things at the same time. One supplement, many problems solved.

Kalk is also cheap – about $11 for a gallon of the stuff at Bulk Reef Supply. I have a 100 gallon tank and I have yet to burn through a gallon of Kalk in the past 9 months that I’ve been running it. For the price, you can’t beat that. Its not even worth trying to be cheap and make your own Kalk for that price.

Of all the things I’ve added to my tank over the years, Kalk has been the one that I easily say had the most beneficial results to my tank. I just wish I had started running it earlier as I could have saved lots of SPS corals and lots of headaches trying to figure out what was wrong with my tank.

Note: If you go overboard with Kalk, you can really screw up your tank. Tomorrow I’ll show you how to run Kalk safely so that your tank shines, not suffers.

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Comments for this article (5)

  • ScottA says:

    I can’t find anywhere in the chemistry of Kalkwasser that would support Alkalinity.. What am I missing? Kalkwasser is calcium hydroxide. How can it affect Alk?

  • Scott…kalk is calcium hydroxide (CaOH). When it hits water, it becomes Ca++ and 2OH-. The OH- is hydroxide = alk

  • ScottA says:

    AHH, You rock, thank you! That makes perfect sense!

  • Alex says:

    Regarding the “sludge line” with kalk in your ATO container do you just toss that part of the solution when you get to it because you don’t want it in your tank or can you use it for something else? Thanks for the great help and advice!

  • Victor Padron says:

    Hi my name is Victor ,how can I dose my 100 gal with kalk?

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