The 900's or the 1200's, I had a 55 that I used two 1200's on and it worked fine. Just one on my 90 tends to blow some sand around. As you can see below if energy bill is a concern the 900's would be the way to go and it never hurts to have an extra one handy. I would suggest at least two for the tank up to and including 4 for a 90 depending on how you have it plumed and the type of return pump/power you have. Also one for mixing your salt mix for water changes.
Maxi Jets Wattage:
600 = 7.5 watts per hour
900 = 8.5 watts per hour
1200 = 20 watts per hour!!!
Model V/Hz Consumption
(in watts)
Maximum
Flow
Maximum
Pumping Ht.
Manufacturer Suggested Retail Price*
l/h g/h meters inches
MP400 120/60 5 400 106 .73 29 $27.90
MP600 120/60 7.5 600 160 1.35 53 $32.85
MP900 120/60 8.5 870 230 1.17 46 $38.40
MP1200 120/60 20 1110 295 1.74 69 $42.85
But you can get them for much less on line
Thomas