DIED some bits and pieces of the puzzle. I would say no as TDS and conductivity go together but not necessarily with high or low alkalinity.
Soft water, by definition, is water which contains very little dissolved divalent cations, specifically, calcium and magnesium, whereas hard water contains high concentrations of these. Water that contains less than 35 mg/L calcium/magnesium (equivalent to about 90 mg/L calcium carbonate or 5 German degrees) is generally considered soft, whereas water containing more than 175 mg/L calcium (equivalent to 446 mg/L calcium carbonate or 25 German degrees) is considered hard. Despite the much confused state of misinformation prevalent in the hobby, hardness has absolutely nothing to do with carbonates. The terms “permanent” and “general” hardness and “carbonate” hardness are obsolete and should be discarded. “Permanent” or “general” hardness is true hardness; "carbonate" hardness is not hardness at all but alkalinity. Conductivity is another parameter that confuses the picture even more. A solution of sodium chloride has high conductivity, but no hardness or alkalinity. A concentrated solution of calcium chloride is very hard, but has no carbonate or alkalinity, but has high conductivity. A concentrated solution of sodium bicarbonate or sodium diphosphate has a very high alkalinity, but no hardness, but high conductivity. Hardness, alkalinity, and acidity contribute to conductivity, but conductivity is not any of them. Conductivity is a measure of the water's ability to conduct an electrical current and reflects the concentration of dissolved ions. Hardness is assessed by measuring calcium and magnesium. Historically, hardness was an assessment of water’s ability to precipitate soap, a property directly dependent on the calcium and magnesium concentrations. The problems arise with test kits and conventions that report hardness as some unit of calcium carbonate. Worse, some so-called hardness test kits actually measure alkalinity. The consequence of this is that many a hobbyist confuses hardness with alkalinity, a measure of the water's ability to resist a drop in pH, calcium carbonate or calcium oxide. To avert this problem, manufacturers and hobbyists should avoid the usage of units that utilize calcium carbonate or calcium oxide as a point of reference. Forget grains or mg of calcium carbonate! Forget German degrees or KH! Hardness should be expressed for what it is, a concentration of divalent metal ions as mg/L. Likewise, alkalinity should be expressed for what it is, the ability to resist change in pH on the measured addition of acid, meq/L. An often overlooked parameter is acidity, which is a measure of the water's ability to resist change in pH on the addition of base. Likewise, acidity should be expressed for what it is, the ability to resist change in pH on the measured addition of base, meq/L. Taken together, acidity and alkalinity constitute the buffer capacity of the water, the ability to resist change in pH from either direction. The assessment of buffer capacity should be as important as the measurement of pH, since rapid change in pH poses a greater hazard than does pH itself. Conductivity is of questionable usefulness: hard water will always have high conductivity, but high conductivity does not necessarily mean hard water; high alkalinity will always give high conductivity, but, again, high conductivity does not necessarily mean high alkalinity. Conductivity tells you how much dissolved ions are in the water, but does not tell you anything about what kind they are. Any dissolved substance that ionizes will raise conductivity: sodium, calcium, chloride, sulfate, even tannic acid.
http://aquanic.org/publicat/state/il-in/as-503.htm http://srac.tamu.edu/tmppdfs/13452410-46...bcb0bc2aa2d4c34 High TDS levels generally indicate hard water, which can cause scale buildup in pipes, valves and filters, reducing performance and adding to system maintenance costs.
Electrical conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the ability for that water to conduct an electrical current, which can be measured using a conventionl conductivity meter. When correlated with laboratory TDS measurements, electrical conductivity provides an approximate value for the TDS concentration, usually to within ten percent accuracy.
Conductivity is a general indicator of productivity. It is the ability of the water to conduct an electrical current. A high conductivity indicates significant amounts of dissolved substances in the water. Conductivity is reported in units of microhos per centimeter of water at 25o due to the influence of temperature on conductivity. This is called specific conductance or specific conductivity.
The specific conductance in the surface waters of Fumee Lake was 272 microhos/cm, and 265 microhos/cm for Little Fumee Lake. These values are typical for lakes having relatively hard water.
Alkalinity
Alkalinity is the ability of water to neutralize acids. It is generally caused by the presence of carbonates, bicarbonates and hydroxides produced by rock - limestone, for example - being weathered by water. Alkalinity is expressed as milligrams per liter calcium carbonate; low alkalinity water has less than 75 mg/liter, high alkalinity water has more than 150 mg/liter.
Hardness
Hardness is a measure of calcium and magnesium ions. Hardness measures are often similar to alkalinity. Hard water lakes are usually more productive than soft water lakes. Hardness is expressed as mg/liter calcium carbonate with soft water ranging from 0 - 75 mg/liter and hard water from 150 - 300 mg/liter.
pH
The concentrations of hydrogen ions in water is expressed as pH. The pH scale ranges from 0 (very acidic) to 14 (very alkaline) with 7 being neutral. Most aquatic plants can tolerate a reasonable pH range but they function best when the pH is around 7.