Fill about 1-2 tea spoons of calcium hydroxide in 5 liters (1 US gal.) R.O. water (distilled water) in a clear canister. Close the canister tightly and shake it. After a while the sediments has settled. Now use the clear lime water not the sediments.
Put the solution very slowly into the aquarium (drop by drop) to prevent a pH disaster. Do not store the solution; it gets old very quickly. Please control the pH of the aquarium water: it should not be over 8.5. If you use the lime water in a lime water reactor please read its instruction manual.
Calcium hydroxide and its solution are very corrodent. Please store it out of the reach of children. If you get contact with the material or solution (for example eyes) wash with clear water and go to an doctor. Take the label to the doctor.