I have a 250 gal spa, and the filter unit is leaking from a
crack around the outlet hole. The filter is a Mytilus 70C, which has a 60 sq ft
filter area (despite the 70C name…). Of course, it has long since been
obsolete, and I don't think I can find a replacement housing, so I'll probably
have to replace the whole filter unit.

I've been looking at the Pentair Clean and Clear units, but
they only come in 50 and 75 sq. ft. sizes, and the 75 is about twice the cost
of the 50. Can I use a 50 on my spa? The current water pressure is around 10
psi and the pump is 1 HP, if that matters.

I'm also a little unclear on dimensions. My piping is
1.5" PVC. It's hard to find dimension specs for the inlets and outlets on
the Clean and Clear units, but I've seen one reference to 2". Can I just use some sort of adapter to make it fit?