The mini NANO  arctica chiller can be used on many of the smaller sized tanks to keep them cool and the temperature stable, Rated up to 40 gallons many people use this guy on the nano cubes.

Now can be used with the new 28 gallon hqi model as well that JBJ just came out with.  This chiller has a pretty small footprint so will fit in the new 28 gal HQI cabinet stand as well