Bulk Reef Supply

Pharma Kalkwasser (Calcium Hydroxide)

Grouped product items
Product Name Qty
Pharma Kalkwasser 2 Pounds

SKU: 210812

In stock


- +
Pharma Kalkwasser 4 Pounds

SKU: 210813

In stock


- +

Ultra-pure Kalkwasser for Reef Tanks!

BRS Pharma Kalkwasser is not your typical calcium hydroxide. It is made from an ultra-pure source that contains extremely low amounts of aluminum and compared to traditional kalkwasser you can actually see the difference. If you are adding Kalk to your ATO reservoir or a reactor, you will find that BRS Pharma Kalkwasser mixes faster with fewer impurities and is even more potent than the others, meaning you will not have to use as much, saving you money in the long run.


Two Sizes Available:

  • 2 Pounds
  • 4 Pounds


Using Kalkwasser (Calcium Hydroxide)

Kalkwasser is the easiest method to maintain calcium and alkalinity levels in a reef aquarium not to mention low cost. With a few different methods to implement it, if your corals are growing and you need to add calcium and alkalinity, you will more than likely find multiple benefits from using kalkwasser. Being the only way to add calcium and alkalinity from a single solution along with helping elevate the pH of your aquarium to helping purify your ATO water even further, there are plenty of reasons to add kalkwasser to your ATO reservoir or set up a Kalk reactor or drip system. By far the most common application for kalkwasser is by adding it to your tanks top off reservoir and then relying on the auto top off system to deliver small amounts of saturated kalkwasser solution throughout the day. 


We suggest using BRS Calcium Chloride, BRS Sodium Bicarbonate, and BRS Magnesium for General Adjustments to elevate and balance your aquariums parameters before using Kalkwasser.


How to Use Kalkwasser with an ATO System

Step 1. Test and adjust your aquariums calcium, alkalinity, and magnesium levels using BRS Calcium Chloride, BRS Sodium Bicarbonate, and BRS Magnesium for General Adjustments. 

Step 2. Start by establishing the proper amount of kalkwasser to mix into your aquariums top off water reservoir. 

  • Low Demand - 1/2 teaspoon per gallon of top off water
  • Medium Demand - 1 teaspoon per gallon of top off water
  • High Demand - 1 1/2 teaspoons per gallon of top off water

Step 3. With RODI water fill your top off reservoir & mix in the proper amount of kalkwasser then allow the solution to settle for 30 minutes before using.

DO NOT OVERMIX: Excess mixing and air contact will decrease the potency of kalkwasser.

Step 4. Place your ATO systems pump or intake line is place 1/2" to 1" above the base of your reservoir, ensuring only the clear slurry is being dosed. 

Step 5. Activate your ATO and monitor the pH of your aquarium as the kalkwasser solution is being dosed, not exceeding increases of 0.20 pH. Your ATO should be pumping water into a high flow area of your sump or display tank to help prevent precipitation. Adding kalkwasser too fast may result in precipitation rendering it ineffective. 

Step 6. Monitor your aquariums calcium and alkalinity daily, adjusting the strength of the kalkwasser solution in your top off reservoir as necessary. 


Note: We highly suggest using a pH controller to prevent against pH spikes and overdosing. 


Refilling The Reservoir

Simply refill your container with fresh RODI water and add the proper amount of kalkwasser per gallon of new RODI water and mix. It is recommended to clean your ATO reservoir regularly, though you do not have to every time you replenish your ATO container.


Maximum Dosage - 1 1/2 teaspoons per gallon of top off water

One of the limitations of kalkwasser is its 1 1/2 tsp. per gallon saturation point. Anything more than that will simply fall to the bottom of your reservoir and become essentially useless. If your aquarium is requiring more calcium and alkalinity added than what kalkwasser can keep up with there are a few solutions; 

  • Start 2-part dosing
  • Increase your aquariums evaporation rate with fans
  • Vinegar method (experts only)


Pharma Kalkwasser Instructions


How Does Kalkwasser Work?

Kalkwasser or Calcium Hydroxide Ca(OH)2 when mixed with fresh RODI water contains a perfect balance of alkalinity and calcium ions that can be added to your aquarium to help supplement what your corals consume when they grow. It is pretty easy to see where the calcium is derived from but the alkalinity can be a little more difficult to see, and when Kalkwasser is added to your saltwater tank a simple reaction takes place converting the hydroxide into available bicarbonate ions. Essentially the CO2 in your water and atmosphere will react with the hydroxide ions creating bicarbonate ions and increasing your tank's pH, due to less available carbon dioxide.

Ca(OH)= Kalkwasser

OH- + CO2 = HCO3 = Bicarbonate

OH- + HCO3 = CO3-- + H20 = Carbonate + Pure Water


Want to see how BRS Pharma Kalkwasser stacks up against the others?


Kalkwasser ICP-MS Results

More Information
SKU Kalkwasser (Calcium Hydroxide) - Bulk Reef Supply
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Product Questions

can kalkwasser be used in freshwater aquarium?
Question by: Diego Galvan on Jan 13, 2023, 7:24 PM
Yes, Kalkwasser can be used in freshwater aquariums but it is not common.
Answer by: William Reed (BRS Staff) on Jan 16, 2023, 7:52 AM

I have the Neptune ATO in a 5 gallon ATO WaterBox ATO chamber in the Sump.

Can I mix this into a bucket in a low dosage and have the Neptune ATO refill as the ATO water?
Question by: Matt Eakin on May 30, 2019, 7:37 PM
Hey there,
Correct! Along with that we went ahead and provided a spotlight video below. Happy Reefing!

Kalkwasser Spotlight
Answer by: Mark Schlough on May 31, 2019, 10:09 AM
The bags of PHARMA KALKWASSER are sold per pound, and the dosing instructions are by volume (teaspoons.) Can you give us an idea of how many teaspoons are in each bag?
Question by: Seth on Jan 28, 2019, 1:52 AM
Thanks for contacting BRS!
The 2-pound bag will contain just under 9 cups of kalkwasser which would be about 141 teaspoons per 2lb bag or 282 teaspoons per 4-pound bag, but this powder can be compacted so the actual number may differ based on how you measure it. Have a great day!
Answer by: Noah on Feb 7, 2019, 11:54 AM