Hydrofarm elec thermostat ??

I hooked it up to my UTH and set it for 89 degrees Fahrenheit. Why won't this thing set to 89, it just seems to stop at like 85. I put the thermometer part in the tank about 2/3 of the way away from the cool side and about 1/2 height wise in the tank ...I don't get what's going on...this is ridiculous.

please some help

the temperature probe for the hydrofarm should be outside the tank between the glass and the heat pad. And all thermostats will have a temperature swing. For example, if you have it set to 90 F, it will turn off at 91, and will not turn back on until it drops down to 88. The trick is to set the thermostat to a temperature that ensures it will heat to the desired temperature (which may be higher or lower than the digital display on the THERMOSTAT). That's why you need a thermometer/heat gun too.

Wait I'm super confused. You want it to control your UTH so you put the probe on the cool side 2/3 of the way down? How do you expect it to control the UTH if you don't put it on the UTH? Maybe I've mistaken something in your post.

Ok I switched it up and put it under the heat pad under the tank between the glass and heater.I was confused on how to use it...

meph I got what your saying,thnk you for the help.
Now I'm looking at it and the temp on the hydro farm has rose to 101 degrees but I have the thermostat set at 91. Idk what is going on,the pad seems to have started cooling down..I feel like a fool,when tis should all be so simple

i have to get a heat gun also,I will asap