ATJ's Marine Aquarium Site - The Lab

The purpose of this lab is to perform a simple evaluation of three different brands of calcium hydroxide:

Seachem Reef Kalkwasser (@ $45.95 for 1 kg)
InstaKalc^TM Calcium Hydroxide (Kalkwasser) ( @ $33.75 for 1 kg)
"LIMIL" Hydrated Lime (@ $5.70 for 20 kg)

Methods

The "Kalkwasser" was prepared in 3 1.25 L soft drink bottles.

Each bottle was washed with white vinegar and thoroughly rinsed with RO water.
RO water was added to each bottle until the water level was a few centimetres from the top.
A plastic teaspoon was used to measure the quantities of calcium hydroxide. Each sample was placed in the teaspoon and leveled with a knife in an attempt to ensure consistency. The actual quantities added was not important as long as each sample was approximately the same quantity.
RO water was added to completely fill each bottle and the bottles were capped.
Each bottle was thoroughly shaken and left to stand for 60 minutes.
The solutions were observed for clarity and amount of sedimentation and pH and calcium concentration was measured.
A second sample of the same approximate quantity was added to each bottle, the bottles were recapped, shaken and left to stand for a further 60 minutes.
The solutions were observed for clarity and amount of sedimentation and pH and calcium concentration was measured.

The pH of each solution was measured using a Corning Chek-Mite pH-20 handheld meter. The calcium concentration was measured using a Seachem Reef Status: Calcium kit with each sample being diluted by 50% and the reading doubled. (0.5 mL sample was taken and 0.5 mL of demineralised water added to make up to 1 mL.)

Results

The results for 1 "level teaspoon" of each sample are shown in Table 1.

Table 1: Results after 1 measure of samples.

Seachem

InstaKalk^TM

"LIMIL"

Clarity

Almost clear

Cloudy

Partially cloudy

Sedimentation

Almost none

2-3 mm

<1 mm

pH

12.22

11.74

12.12

Calcium (mg/L)

500

90

470

	Seachem	InstaKalk^TM	"LIMIL"
Clarity	Almost clear	Cloudy	Partially cloudy
Sedimentation	Almost none	2-3 mm	<1 mm
pH	12.22	11.74	12.12
Calcium (mg/L)	500	90	470

The results for 2 "level teaspoons" of each sample are shown in Table 2.

Table 2: Results after 2 measures of samples.

Seachem

InstaKalk^TM

"LIMIL"

Clarity

Cloudy

Cloudy

Cloudy

Sedimentation

2-3 mm

3-6 mm

3-4 mm

pH

12.37

12.13

12.40

Calcium (mg/L)

730

300

730

	Seachem	InstaKalk^TM	"LIMIL"
Clarity	Cloudy	Cloudy	Cloudy
Sedimentation	2-3 mm	3-6 mm	3-4 mm
pH	12.37	12.13	12.40
Calcium (mg/L)	730	300	730

Discussion

The quantity in each sample was chosen such that one "measure" would produce something less than a saturated solution as this should show variation in the samples more obviously. Two "measures" should have produced a saturated solution, however, the calcium levels suggest the solution is not quite saturated. A saturated calcium hydroxide solution should have a calcium concentration approximately 900 mg/L.

As the methods used result in imprecise measurements, no definitive conclusions can be made. However, the evaluation shows trends that suggest that the inexpensive "LIMIL" brand calcium hydroxide should produce similar results to Seachem brand. The amount of sedimentation with the "LIMIL" brand was quite low which suggests either low levels of impurities, or those impurities are quite soluble.

The results of the InstaKalk^TM were not very good. It is possible that this is partially due to the sample being quite old, but even when new there was noticeably more sediment produced.

Last updated: August 11, 2001