provides summary technical info on boron including its algaecidal effects and toxicity. At the 30-50 ppm Borates (measured as ppm Boron) recommended for pools and spas, it should be considered to be a mild algaecide. You should avoid having your dog drinking regularly (i.e. daily) from the pool as this level is at the edge of first symptoms (mostly reduced testicle size in male dogs).
The borates act primarily as a pH buffer, especially effective at buffering against a rise in pH. In pools using a hypochlorite source of chlorine, this can let one lower the Total Alkalinity (TA) level to reduce the rate of carbon dioxide outgassing and therefore reduce both the rate of pH rise and the amount of acid needed to compensate for such rise. If the TA is lowered, the target pH or the Calcium Hardness (CH) level may need to be increased to keep the saturation index near zero (for plaster/gunite/grout pools).
20 Mule Team Borax raises the pH so can be used in place of pH Up (sodium carbonate) products. It will raise the pH with half as much rise in TA compared to pH Up. If one wants to add borates to the pool, then one needs either to add acid along with Borax, use a pH balanced borates product, or use Boric Acid which is more pH neutral (only slightly acidic).
Borates in the water appear to reduce its surface tension, as apparent by a flattened meniscus when doing water tests. This also seems to make the water appear more shimmery. Some people say they like the feel of the water better, somewhat similar to bath salts.
As for the Foundation product, neither borax nor EDTA will remove phosphates. Typically, lanthanum chloride is used to reduce phosphates as lanthanum phosphate is insoluble. Perhaps they are mixing up the Borates ability to inhibit algae or they have lanthanum chloride in the product but do not list it in the MSDS. Also, neither borax nor EDTA is a natural enzyme. EDTA is a metal sequestrant, though not the best one. It may somewhat reduce active calcium levels, though water balance is more readily achieved through adjustment of water chemistry parameters to adjust the saturation index.
The use of borates is particularly useful in a saltwater chlorine generator (SWG) pool since the extra pH buffering helps to reduce the formation of scale on the cathode (where hydrogen gas is produced) and its algaecidal properties may reduce chlorine demand letting one turn down the ontime of the SWG which helps to reduce the rate of pH rise and prolong SWG cell life.