If your float tanks have a vinyl plug, take them out and leave them out for a while and see what happens. The plugs usually have a small relief hole through the center but sometimes it is too small and seals itself off. If taking the plug out corrects the problem, make the holes in the plugs larger. If the float tank has no hole or plug of any type, you can drill a hole that is a little smaller than a stainless steel sheet metal screw and use that has a plug. There will be enough of a gap around the threads to equalize pressures.