The tubes on your Goldish RIB has auto adjusting excess pressure valves. The valves ensure that the tubes never suffers from excessive pressure. 

In climates with high variety in temperature, you might experience a large difference in the pressure of the tubes from day to day. This is due to the density of the air. As you might know from school: How air has A greater density than cold air. 

Therefore, during a hot day the air expands, and the tube might reach its maximum pressure, and the excessive pressure valves let some air out to protect the tubes from damage. When the air cools down, it will take less space in the tube. This might lead to soft tubes. 

You should not use your Goldfish RIB with low pressure in the tubes. That might damage them.