notsolowki:
how could i interface just one of these probes with an arduino and read the numbers from it?HM Digital SP-2 Dual TDS Sensor Probe for DM-1 Dual Inline TDS Monitor – Fresh Water Systems
This one appears to be just a pair of probes. You need the appropriate hardware to produce an AC signal across them, then use that to measure the conductivity. To do that all you basically need a cap and two resistors (this works great, it can give you really stable readings), or you have to wire up a 555 astable and measure the output frequency (my latest attempt for reading an EC probe - this is work in progress).
notsolowki:
or this sensor, https://www.mouser.com/ProductDetail/SparkFun-Electronics/SEN-13322/?qs=WyAARYrbSnberEHb08L3VQ%3D%3D&gclid=EAIaIQobChMIrLCQwrOw2gIVBglpCh1h2gKQEAQYASABEgKdW_D_BwE
This is a soil moisture sensor, not suitable for use in water.