China chillers such as Hailea and Resun cost 3 to 4 times cheaper than their US and European counterparts. However, the most common problem faced by users is that the temperature controller of the china chiller is not robust. It tends to give problem every 1 to 2 years.
There are generally two methods I can think of to improve the condition: -
1) Replace the sensor in the Hailea or Resun chiller with one thermocouple which can be submerge into your tank to monitor the temperature. This can be done but a suitable thermocouple must be used. Personally, I have yet to try this
2) Use an external temperature controller. This temperature controller has a waterproof thermocouple that can be submerge into water. This controller also allows user to adjust temperature with more flexibility. I have manage to make an external temperature controller myself for approx $70.
The items needed to build an external temperature controller: -
1) Temperature controller & thermocouple. I uses the fox brand and I purchase it from Sim Lim Tower for S$60
More information can be found here
2) Three pin socket. This can be bought for approx S$5.
Picture of socket can be found here
3) Power cord. I got this free as I salvage from my old PC
4) Power enclosure. I got this for free as I salvage from old parts. A plastic one made of polycarbonate or ABS will be suitable. Ideally, an enclosure made of UL94V0 material will be ideal. A good enclosure cost about S$15-20 despite cheaper ones are available at $5.
Encloures can be found here
I will take some pictures of my temperature controller shortly.