The problem with the hydrofarms is the probe accuracy is very poor this type of thermostat needs a deceint reasonable accurate thermometer as the one that is with the probe is very poor (+/- 2ºC range that is very close to 4ºF If it reads 90 it could truely be between 86-94 this is a large amount. The reading on the unit cannot be trusted and must be checked with an accurate thermometer. I suggest that you buy at least 3 thermometers 5 would be better and check them against each other and use the ones that read the same and return or dispose of the others. I tend to buy cheap ones for this for obvious reasons I usually pay on ebay between 1-4$ a unit with shipping look up aquarium thermometers.