Figure 1: Bulk Kalkwasser container after standing for 3 days.
I currently have 9 aquaria, 4 of which I dose Kalkwasser (limewater) on a nightly basis. I had been preparing each aquarium's Kalkwasser a night in advance by directly mixing builder's lime with RO (Reverse Osmosis) water in a plastic 2 litre bottle. This was taking around 30 minutes each day and, to ensure a saturated solution of calcium hydroxide, I was using excess builder's lime in the bottles.
After reading Randy Holmes-Farley article on The Degradation of Limewater (Kalkwasser) in Air, I realised that I would have few problems with premixing the Kalkwasser in bulk and decanting the clear saturated solution of calcium hydroxide every few days. This is what I now do.
I have validated the concentration of the Kalkwasser using a conductivity meter. The conductivity of the clear decanted solution is as high if not higher than the freshly mixed (and cloudy) solution. The latter has the same conductivity as the individual solutions I was preparing previously.
I am using a 30 litre drum for mixing the Kalkwasser. I decided on this because it will give me 3 to 4 days worth of Kalkwasser so I only have to mix twice per week. The drum has a tap which is a few centimetres from the bottom of the drum.
I add around 25 litres of RO water to the drum and then add around 120 millilitres of white vinegar to the water. I then add around 30 heaped teaspoons of builders lime, to the water and mix thoroughly with a length of PVC pipe. I top up the water in drum, mix again, and place the lid tightly on the drum.
I place the drum on a shelf with the side with the tap slightly raised to reduce the chances of sediment being drawn out through the tap. While this reduces the volume of Kalkwasser that can be decanted in each batch, the Kalkwasser is clear when poured off. The solution is left to stand for 2 to 3 days before decanting.
Figure 1: Bulk Kalkwasser container after standing for 3 days.
I still dose the Kalkwasser nightly using the 2 litre soda bottles, but with the bulk Kalkwasser the time required to fill each bottle is significantly less and I can prepare multiple (3 to 4) nights bottles in a single operation. I decant the solution from the drum until the water level in the drum drops to the level of the tap. This provides around 28 litres of Kalkwasser, enough for 3 and a half days worth of dosing.
To prepare each bottle, I open the lid on the drum to allow air into the drum and fill each container from the tap on the drum. Each bottle is then capped and either used that night or left for use on the following two to three nights.
The biggest advantage to the new process is the time I save. Instead of spending 30 minutes each night, I only have to spend 30 minutes every 3 to 4 nights, and this includes both the preparation of the bulk Kalkwasser in the drum and the decanting to 14 containers.
As I am only decanting the clear solution, there is no precipitate in the bottles and no danger of the precipitate being added to the tank. I can also use the decanted solution immediately.
Probably the only disadvantage is to my back in lifting the drum onto the shelf.
For information on devices to determine the saturation of Kalkwasser, see What is TDS? by Randy Holmes-Farley.
Last updated: October 12, 2004