I think this chiller is not powerful enough for 2ft, 80liter tank. think u need to get a bigger 1.
this chiller only support max 10-30liter which is max of around 1ft tank. See the link for the spec.
http://www.eastoceansg.com/al30-mini-chiller-for-up-to-30l-tank-p-1668.html
your chiller is working on full load all the time. very fast will up lorry.