I have a 40,000 gallon, 20 x 40 inground pool. I am replacing the 1996 model filter and 6 way valve. I ordered the same filter brand, same model number that is listed on the old filter. Could technology have advanced since 1996 to the point where the filter tank is considerably smaller? I am thinking that the older filter was mismarked by the manufacturer. Can I have anyone's opinion on this? It just doesn't look right.