Celebrating the Awesome Beauty of the Lord's Tropical Reef in a Home Marine Aquarium

Kalkwasser Top-Off System


Since we started measuring water parameters we noticed that both calcium and alkalinity were running consistently low (averaging 380-400 ppm and 2.8-3.0 meq/L respectively). I assumed we needed to add some type of supplement to raise them both but was not sure how. After searching Reef Central looking for ideas I stumbled upon the Reef Chemistry Forum moderated by Randy Holmes-Farley. Randy wrote an excellent article titled "Solving Calcium and Alkalinity Problems". In it I learned that we could dose our tank 24/7 with a solution called "kalkwasser", which is German for lime water. Kalkwasser is aqueous solution of calcium and hydroxide ions that can be made by dissolving either quicklime (calcium oxide, CaO) or lime (calcium hydroxide, Ca(OH)2). Dosing with kalk adds a balanced quantity of calcium and alkalinity. This is an excellent solution since by adding one supplement you raise both calcium and alkalinity at the same time. Furthermore, if you dose the kalkwasser by slowly dripping it into the sump 24/7 you can use it to balance evaporation and eliminate daily manual top-offs!

We chose to implement the same type system as Randy uses for his aquarium. The design invloves using a dosing pump to supply a steady drip of kalk into the sump. The kalk is made in a separate 36 gallon Rubbermade Brute container in our basement. The pump draw the kalk out of the container and sends it to the sump at a steady rate 24/7.

For the pump we purchased a Reef Filler 7GPD (gallons per day) model.


For a source of calcium hydroxide we selected Mrs. Wages Pickling Lime. Sixteen ounce bags are very reasonably priced so we purchased a couple cases to last us a while!


Once we had a sufficient length of plastic tubing we were ready to begin setting up the system. First I mounted the pump on the plywood wall just above the location of the Rubbermade container in the basement. After mounting the pump I connected a length of hose to the inlet side. On the other end of that hose I attached the inlet housing and ceramic weight. The inlet housing has a check valve inside to keep the solution from backwashing into the container when the pump is turned off. The weight is used to hold the hose down near the bottom of the container to ensure you can draw out the maximum amount of solution. The hose was cut to a length that keeps the inlet housing about two inches off the bottom of the container. The extra hose seen in the pictures leading off the top of the pump fitting is the primer drain that leads back to the container. This line is only used when you first start the pump at the beginning to help purge air from the line and pump head in order to get the solution flowing. Once primed the line is shut off and remains unused.


I then attached a more rigid, opaque turbing to the pump outlet and routed it up through the livingroom floor to a fitting arrangement I made in the sump.


Once the entire setup was installed and all the hoses connected I mixed the kalkwasser solution. I first filled the container with about 32 gallons of fresh RO/DI water and then added 2 teaspooons per gallon (1.25 cups) of Mrs. Wages Pickling Lime. It is recommended to leave the mixed solution overnight to allow all the sediment to settle to the bottom. The next morning I carefully skimmed the thin film of kalk sediment off the surface. At this stage the solution was essentially clear and ready for dosing. I truned on the pump and waited for the solution to eventually inch it's way up to the livingroom and begin dripping into the sump. Voila`... the system was running!

Over the next day or so I adjusted the output of the pump to match evaporation. Once adjusted, and as long as the photo period is consistent, there's no need to readjust. One container normally lasts me about 8 days with the current rate of evaporation. Not too shabby! Here's a shot of the entire system in the basement after installation.