My boyfriend and I just got two new guinea pigs last night and they seem happy and very active but I am just wondering how much hay is too much? I filled their hay-ball last night and by this morning it was empty. I filled it again and it is just about empty again. I know hay is an essential part of their diet but how often should I be filling their hay-ball? Thank you! We are new guinea pig owners so any advice would be very helpful 8