I have a 18' round doughboy pool with sand filter. I have been using a Power Pak pump. This is actually the second pump in 3 years. Is there any other brand of pump that I can use with my pool and filter or do I have to use a Power Pak? Our local pool store only sells Power Pak so of coarse that is what the tell us we need, but they are so expensive. I know that there are others out there that are less expensive but I don't know if they will work with our pool. Can anyone help?