Researching cartridge filters for my IG pool. Pool is 16 x32 and about 20k gal. 1HP WMC single speed pump, 1 1/2 PVC for plumbing. Current pool filter is a tagelus TA-60 sand. Using Blue Pearl robotic cleaner and BBB method. From all my readings bigger is better, What sizes should I be considering? What brands are the most troublefree- Pentair, Hayward, Jandy Sta-Rite? Given the 1 1/2 piping would I be defeating the purpose of going to a larger filter (over 320 sqft) other then freq. of cleaning? Finally, any hints on vendors with competitive prices?