I recently purchased a 2000 Kamberra. All the documentation and a call to Mooba verified that this is supposed to be a 40 gallon tank. I fill it up when I get down to 1/8 to 1/4 tank and I have only been able to get 25 gallons in it. Is my float that off or is my tank actually smaller? I hate crusing on empty hoping I have another 15 gallons to play with.