I need a sensor that will work in a liquid with low conductivity in order to trigger a 12v relay. Any ideas ?

Then you'll have to find another way. Possible lanes of inqury:

- capacitive sensor (if the resin has an e_r significantly different from 1)

- optical sensor (if the resin's refractive index is significantly different from 1)

- find/design a float switch that is small enough to work in your gap, yet sufficiently reliable

- measure the weight of the container with the resin (may require a full redesign of your setup)

- if the resin can be "seen" (visually distinguished by a video camera, possibly operating at an optimized wavelength), use machine vision to determine the fill level of the container (slightly more complicated optical sensor, but a lot of work here already has been done for you, e.g. in OpenCV)

- use an ultrasonic distance measurement between some fixed point (either above the liquid level or below - the principle will work either way, but "dry" ultrasonic transducers may be easier to sorce than ones that will work immersed in the resin) and the resin surface to determine the fill height (also used in some cistern level meters) or an ultrasonic level sensor as a switch

I am measuring liquid level.

I cant use any float switch because i cant find any float switch that small enough to fit. (5mm gap)

The small tank gets filled slowly with a pump, pumping UV light sensitive resin. Resin is thick but does have some low conductivity.

I am trying to trigger the relay once conductivity is detected.

So far no luck :(

What exactly does work in a liquid mean? Are you measuring liquid presence or conductivity or something else. Unless the spec sheet says so, the sensor is extremely unlikely to be able to deliver a relay triggering signal. Intermediate circuit that senses a sensor signal going in a direction and generates a clean 12v step at the appropriate time would work better.

no