ya true as the smaller the tank the temp will rise fast as what u said bad ventilation ''binosage''
comycus what is the gallon of your tank and how many pump u use?? u may try to set the temp to different by 1.5 to cut in if your target is to get a result of 27 means max 28.5 that will take longer for the chiller to cut in another thing is that condition of ur chiller example is the fan still fast enough to cool down the condenssor or is the condenssor dirty even the frt ventilation of the chiller is it block with thing??/