I have a 18x33 oval above ground pool. I'm trying to buy the best but cheapest SWG I can. I was looking at the Aquatrol but they are only rated for 18,000 gallons so I thought that wasn't enough. Can I use the Aqua Rite in my AGP? Hayward's website says these are for inground pools only, but does this really make a difference? Can you recommend which SWG for my pool size? Thank you.