..... diy I would say 1.5 no smaller. I have one on my 180 gallon cichlid aquarium I never have a problem out of it and no lift pump. I used it on my reefs before I drilled. I found that if I used a bigger intake. Like a 2" and reduced it it would cause less of a fluctuation in aquarium water level. If you use a lift pump the valve tends to become clogged quickly so care to keep clean. Mine would suck up a piece of algea or small animal...
75 and 36b reef tanks
180 new world cichlid tanks