I am doing a research regarding amphibian population in tea estates. I found range of pH is 6.1 - 4.2 an range of EC 5-20 in water sources where tadpoles are living.
Both low pH and high salinity can impact on tadpoles, for example, Andren et al. (1988) reported mortalities and deformities of tadpole’s (Swedish brown frogs) at low pH (reference 1), whereas higher salinities caused delayed metamorphosis (at 8 ppt salinity), and increased mortalities (at 10 ppt) of the Puerto Rican Crested toads (see reference 2)
Reference
1.C. Andren, L. Henrikson, M Olsson and G Nilson. 1988. Effects of pH and aluminum on embryonic and early developmental stages of Swedish brown frogs Rana arvalis, R. temporaria and R. dalmatina. Holarctic Ecology. 11: 127-135.
2. Effects of salinity on the growth and survival of tadpoles of the Puerto Rican Crested toads. http://repositorio.upr.edu:8080/jspui/bitstream/10586%20/203/1/poster%2049%20esac%202009.pdf
Read: Viertel, B. (1999): Salt tolerance of Rana temporaria: Spawning site selection and survival during embryonic development (Amphibia, Anura). Amphibia-Reptilia 20: 161-171
Suggested reading: Sadinski, Walter J., and William A. Dunson. "A multilevel study of effects of low pH on amphibians of temporary ponds." Journal of Herpetology (1992): 413-422.
Sanzo, Domenico, and Stephen J. Hecnar. "Effects of road de-icing salt (NaCl) on larval wood frogs Rana sylvatica." Environmental Pollution 140.2 (2006): 247-256.
BRUNELLI E., TRIPEPI S. – The effects of low pH acute exposure on survival and gill morphology in Triturus italicus larvae. Journal of Experimental Zoology, 303A (11), 946-957, 2005.