Digital Inline TDS Titanium Series are the smallest inline TDS available on the market. They allow hobbyists efficiently to real-time monitor the RO/DI water quality. The series includes Titanium One (one probe), Titanium S1 (one wired probe), Titanium S2 (two wired probes) and Titanium S3 (three wired probes). All of them use titanium probes, which perform excellent corrosion resistance. Also, they are very easy to install with a ¼” Push Connect Union Tee (included).