PH is a way of measuring whether aquarium water is acidic or basic (alkaline). It is measured on a scale of 0 to 14, with 0 to 7 considered acidic and 7 to 14 considered basic or alkaline.
Most freshwater tropical fish do best between 6.8 and 7.8, however, some species come from areas where pH can be significantly higher or lower than these values. For example, cichlids from the Rift Lakes of Africa are used to a pH between 8.0 and 9.0, whereas Cardinal tetras from the Rio Negro in South America live in water with a pH below 5.5
When setting up a new aquarium, test your tap water to make sure the pH and other water parameters are within the correct range for the animals and plants you plan on keeping.
TDS stands for Total Dissolved Solids, what this means in real terms is that a TDS meter will measure all negative (anions) and positively charged ions (cations) that are present in water.
Many chemicals and pesticides make it into our tap water due to land run off, sewage and industrial activity; a high TDS reading may give an early warning to deterioration of local or seasonal tap water that may otherwise go unnoticed.
Although Ro units are extremely efficient at removing unwanted ions from water residual amounts of very small compounds such as ammonia and silicate can still find their way through the minute pore size of the membrane . These compounds can harm sensitive fishes and invertebrates as well as provide nutrients for unsightly algae.
For this reason we highly recommend that tap water and RO effluent TDS is regularly monitored with TDS meter.