Conversion Factors - T.D.S & Useful Information

Table Version

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Total Dissolved Solids Table

Resistively Mog
0.056 18.000 0.028 0.002
0.063 16.000 0.031 0.002
0.071 14.000 0.036 0.002
0.083 12.000 0.042 0.002
0.100 10.00 0.050 0.003
0.133 7.500 0.67 0.004
0.200 6.000 0.100 0.006
0.600 2.000 0.260 0.016
1.000 1.000 0.600 0.029
1.333 0.750 0.667 0.039
2.000 0.600 1.000 0.068
4.000 0.260 2.000 0.117
10.000 0.100 5.000 0.292
20.000 0.050 10.000 0.686
40.000 0.025 20.000 1.170
80.000 0.013 40.000 2.339
100.000 0.01000 50.000 2.924
200.000 0.00500 100.000 5.848
500.000 0.00200 250.000 14.620
1000.000 0.00100 500.000 29.240
2000.000 0.00050 1000.000 58.480
5000.000 0.00020 2500.000 146.1990
10000.000 0.00010 5000.000 292.398

Other Conversion Factors for Water Treatment
  • One (1) Cubic Foot equals 7.48 US Gallons.

  • One (1) Cubic Foot equals 28.32 Liters.

  • One (1) US Gallon 3.785 Liters.

  • One (1) Liter equals 2.2 Pounds.

  • One (1) Liter equals 61.03 Cubic Inches.

  • One (1) Cubic Foot equals 1,728 Cubic Inches.

  • One (1) US Gallon equals 8.33 Pounds.

  • One (1) Grain per Gallon equals 17.1 PPM.

  • One (1) PSI equals 2.307 feet of head for water.

Total Dissolved Solids

One of the important measures of water quality is the amount of dissolved minerals in the water which is called Total Dissolved Solids (TDS). TDS is typically measured by devices which quantify how the water sample conducts an electrical current. All the measurements with the exception of the GPG figures are electrical measurements. The different units are used to make it convenient to express the Total Dissolved Solids (TDS) values.

The most important thing to remember is that the all the units measure the same thing and are all done by electrical current conduction. The measuring instrumentís internal electronics make the conversions to the unit of measurement shown on the dial.

Chart Definitions

Conductivity is measured in MS/cm2 which is Micro-Siemans per Square Centimeter. This measurement is used more commonly for Untreated City Water and often in Cooling Tower and Boiler Water Conductivity.

Resistivety is measured in Meg-Ohm/cm2 which is Million Ohms per Square Centimeter. This measurement is used commonly in Treated Deionized or RO/DI Water Systems for High Purity Applications. The reason that Resistivity is used is that Conductivity at High Purity results in low readings which are difficult to discern.

TDS. measured in Mg/L, translates to dissolved Milligrams per Liter of solution. To make sense out of all the different measurement units, we try to convert them all to this unit.

TDS, measured in GPG, translates to dissolved Grains per Gallon of solution. This is the old avoirdupois system in Grains, ounces pounds and tons. It is commonly used to measure water hardness and resin capacities in Grains per Cubic Foot(FT3) of Resin.

Useful Information

  • one cu ft (cubic foot) of sea water = 64 lbs, 29.02 k, 7.5 gal, 28.4 L, 1728 cu in (cubic inches)

  • one gallon of sea water = 8.5 lbs. 3.86 k , 231 cu in

Alkalinity - measures the amount of acid required to neutralize the alkaline salts such as carbonates or bicarbonates present. Recommended level 8.0 - 12 DKH. The buffer is the sum total of the carbonates and bicarbonates in the water, these constitute the buffering capacity of the water, also acid binding capacity. This is in essence the ability of the water to deal with the continuous production of acids of all kinds, including course, the carbonic acid generated by the addition of CO2. Should this buffering capacity become too low, the ph will start falling, and the fall is the pronounced, the lower the buffer or carbonate hardness is.

Hardness - refers to the total amount of dissolved mineral salts in water such as carbonates, bicarbonates and sulfates of calcium, magnesium and other salts. To find the calcium ion concentration you need to multiply the calcium carbonate equivalents value by 0.4. Aquarium levels have ranged from 288 to 390 mg/L, you should use calcium chloride (calcium chloride di-hydrate) to raise the calcium level to between 420 and 450 mg/L. Once the desired level of calcium is attained you can then use the calcium hydroxide solution to maintain it.

Carbon Dioxide - is dissolved in water either as CO2 of H2CO3 (carbonic acid). Carbonic acid disintegrates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The bicarbonate ions eventually dissociate into carbonate ions (CO3-) and hydrogen ions (H+). All these are so called equilibrium or reversible reactions - that is, they move forward or are reversed according to prevailing conditions.

Dissolved Oxygen - in sea water at 75 degrees F will contain about 6.8 mg/L of dissolved oxygen at 100% saturation. Under increasing temperature, oxygen decreases by 10% for every rise of 9 degrees F.

Phosphate - inorganic phosphate in marine water consists of hydrogen phosphate HPO4, di-hydrogen phosphate H2PO4 and phosphate ion PO4. These phosphates are commonly called "ortho-phosphate" and is the primary source of phosphate for marine algae. Recommended level below 0.05ppm PO4.

Total Dissolved Solids- actually measures conductivity but is calibrated with sodium chloride solution so that TDS is expressed in ppm of NaCl. Conductivity is calibrated with potassium chloride but is expressed in micro siemens.

Formulas for converting Conductivity and Total Dissolved Solids
TDS = Conductivity Reading/1.5
Conductivity = 1.5 X TDS Reading

Salinity - acceptable levels, 25 ppt - 1.018 SG, 35 ppt - 1.026. Freshly mixed s.w. has a orp value 230 - 245. SALTS which make up seawater in descending order of concentration - sodium chloride (NaCl), magnesium chloride (MgCl2), magnesium sulfate (MgSO4) calcium sulfate (CaSO4), potassium sulfate (K2SO4), calcium carbonate (CaCO3), potassium or sodium bromide.

pH - expresses the relative proportions of acid hydrogen ions (H+) and alkaline hydroxyl ions (OH-), when CO2 decreases the equilibrium of the pH shifts towards the right or alkaline side of the scale (water becomes more alkaline). When dissolved CO2 increases the pH drops and the water becomes less alkaline or more acid.

Reverse Osmosis - drops the ionic strength of the feed water by filtering out the ions of the dissolved salts present. As a result of this, the hardness is also reduced. Reverse osmosis is a filtering process which removes dissolved salts and molecular compounds present, producing a softer water as a product.

Deionization - reduces the ionic strength of the water by removing all the dissolved salts. A deionizer is commonly composed of two separate cylinders: a cation cylinder which removes all of the cations; and the following anion cylinder which removes most anions if it is the common weak anion resin. The weak base anion resin will not remove the bicarbonate ion, HCO3-. The acid from the cation resin causes the bicarbonate ion to hydrolyze to free carbon dioxide, CO2. To remove the CO2, the water must be strongly aerated for at least six hours before it could be pumped into the fish tanks.

Ozone - 1 mg. of ozone per 1 gal. of water with an air dryer. 2 mg. of ozone per 1 gal. of water without an air dryer.

Hydro-Logic Incorporated
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Gloucester City, NJ 08030
Phone: (856) 742-8300
Fax: (856) 742-7623
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