One of the common gripes about these spa’s is the fact that when you use the bubble massage system you can’t use the heater at the same time. The bubbles have a 30 minute auto shut off and in that time the temperature can drop a few degrees. The bubbles going through the water can make it feel a bit cooler too. To be fair this is an issue with most portable hot tubs with bubble jets. It’s easy to switch the heater back on as soon as the bubbles are finished but the temperature only rises a few degrees an hour.