I have an old Hayward Swimpure Plus system for my 15,000 gallon pool. I need to replace the old cartridge but all I can find are the newer T-Cell 3's, 9's, & 15's. Although my cartridge looks like them there is no T-Cell enumerations as it predates that numbering system. I have firmware version 1.4. What can I do? I hope the answer is not replace the whole system.