A TDS meter is a small hand-held device used to indicate the Total Dissolved Solids in a solution, usually water. Since dissolved ionized solids, such as salts and minerals, increase the conductivity of a solution, a TDS meter measures the conductivity of the solution and estimates the TDS from that reading. For Shrimps tank safe TDS value is below 100.
Aquarium filters can only catch what comprises TSS (Toal Suspended Solids), which are material things such as plant matter or fish waste. High concentrations of TDS can reduce water clarity and decrease photosynthesis in aquatic plants.