Mike wrote:
The water comes down over the pads so fast that it dribbles over the
louvres and on to the roof, and then down to the side of the house.
Should I switch to pads that are more tightly packed? Should I buy a
smaller pump., say 4500?

I haven't seen the paper pads, but suspect that their pores might
get gummed up with minerals if your water is hard.

Sounds to me like you want something LESS tightly packed, like
the thick pads made of aspen noodles (like the noodles put on top of
chow mein). These have plenty of space for the water to enter and wet
the fibers, and are available in a range of sizes, say 28"x28" up to
32"x32" at least.