Water testing

See also: Chemical Guide

SALINITY METERS SALINITY METERS measure the salt in the Total Dissolved Solids in ppt or ppm and give a very accurate reading of the salt content. Very useful for owners of salt-water spas, and pools with salt-water chlorination systems. These instruments will provide readings on a scale from at least 2000 to 7000 ppm and are far more accurate than test strips or cheap digital TDS meters.
For 4,000 ppm you need 40 kg of pool salt per 10,000 litres (10 m3, 2,642 US gallons) Salt is a part of Total Dissolved Solids, only a genuine salt meter will accurately display the salt level. Cheaper TDS meters display the total of salt and all other dissolved solids. For starting up, a typical average sized domestic pool, say 4 x 10m with an average depth of 1 metre (from about 0.7m to 1.40m deep) will need 160 kg or 7 x 25 kg bags of special TRS pool salt, but do not forget to include the volume of your balance tank (if any). Only special pool salt will provide a reasonably accurate ppm reading.

pH METERS: pH is a measure of the activity of the (solvated) hydrogen ion. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. The pH, which as every pool owner knows - or should know - must be kept within 7.2 - 7.6. What everyone does NOT know is that it is even more important to maintain the pH than the chlorine level - if the pH is not right, the chlorine won't work properly.

ORP TESTERS measure the ORP, also known as redox potential, oxidation / reduction potential, and measure the Chlorine in a fundamentally different, and far more accurate way than traditional PPM Test Kits with reagent drops, tablets, powders, or test strips. Operators of large or commercial pools must realize that basic test kit measurements are insufficiently accurate and can differ fundamentally from ORP readings.

COPPER TESTERS are essential for pools that are permanently disinfected by ionisers (Naked, etc.) or chlorine substitutes such as PurePool or NanoKleer, and when copper based algicides are used regularly. Test kits are available by Hanna electronic-photometric checkers, and Microtest (marketed by Naked) titration kits. The required concentration for using a copper based disinfection system is 0.2 – 0.5 ppm. Occasional shocking with small ammounys of chlorine may be required.

ALKALINITY TESTERS are used for testing the alkalininty beyond the parameters of the normal pH range when normal dosing with pH Minus or pH Plus does not result in a stable pH. Ideal Total Alkalinity Levels: Concrete Pools: 80 - 150ppm. Total Alkalinity should not be confused with pH, although the two are closely related. Total Alkalinity determines the speed and ease of pH change, it is measured in ppm. Low Total Alkalinity can cause unstable pH levels. This causes an inability to keep the pH constant and may cause staining, etching and corrosion of metals. High Total Alkalinity will cause constantly high pH levels. TREATMENT: If the total alkalinity is below 50 ppm, add SODIUM BICARBONATE (not Soda Ash) or Magnesium Oxide (MgO, PH Flats). Standard dosage: Sodium bicarbonate - 6kg per month per 100 M3 of water.   Operators can also feed calcium chloride at the appropriate dosage to achieve a calcium hardness level that satisfies the 25,000 rule. New pools that have fresh plaster, grout or concrete can be maintained at a Saturation Index level closer to 30,000 or 35,000 for the first six to 12 months while the surface finish is still new.

HARDNESS TESTERS are are used to determine the level of calcium in the water. For pools (or homes) using well water in areas where the aquifer is in sedimentary rock (limestone), a hardness test is essential to prevent damage to swimming pool equipment, especially pumps, heaters, and salt water chlorinators. Ideal Calcium Hardness Levels: Concrete Pools: 200 - 250ppm Fibreglass/Vinyl Pools: 150 - 190ppm
In addition to pH and Total Alkalinity, Calcium Hardness must be kept in balance so that your pool water does not become too corrosive or end up scaling the surface of your pool. Since calcium ions cannot be effortlessly removed from pool water, it is important to know the calcium substance of the source water (make-up water). In some cases iot  may be necessary  to  insatll a water softening  system.

Total Alkalinity and Calcium Hardness must be considered together, because one influences the other. Temperature, pH, total alkalinity and calcium hardness are four major factors used to calculate the Saturation Index, which is a measure of water’s tendency to scale or corrode surfaces that it touches. The Saturation Index must be considered in picking a target for total alkalinity and calcium hardness. But in pools maintained between 25.5°C and 29.5°C and at pH levels of 7.2 to 7.6, temperature and pH can effectively be considered constants, not variables. This somewhat simplifies calculating the Saturation Index. TOTAL ALKALINITY should generally be between 50 and 125 ppm and calcium hardness between 200 and 500 ppm. To ensure these factors’ levels fall within the appropriate range, total alkalinity times calcium hardness in ppm should approximately equal the number 25,000 (+/- 10%) For instance, if total alkalinity is 50 ppm, calcium hardness should be about 500. Note that this 25,000 rule only works if the pH is between 7.4 and 7.6 and the temperature is between 25.5°C and 29.5°C. Makeup water characteristics, bath load and chemicals used affect precisely where in this total alkalinity and calcium hardness range a pool is operated. Under normal operations, total alkalinity tends to drop in most pools because it is reduced by gas chlorine feed and hydrochloric acid (or pH Minus) feed. To counter these constantly declining levels, total alkalinity’s lower levels should be maintained between 50 and 80 ppm and countered with higher calcium hardness. If total alkalinity falls below 50 ppm, operators can feed calcium chloride at the appropriate dosage to achieve a calcium hardness level that satisfies the 25,000 rule. CALCIUM HARDNESS, on the other hand, is a comparatively stable factor in pool water chemistry.