Since you have a canopy, maybe you could try adding a few fans to the interior of the canopy, blowing over the surface of the water, to reduce the temperature. You could set them on a timer outlet so they only run when the halides are up. In all likelihood this will increase your evap... do you have an auto top off system on your tank?
Chillers get pretty pricey, even for the 1/5 and 1/4 hp models. See if you can't solve it with a couple of $20 fans. You might luck out.
Hrm. Looking at the above page, I see that you do indeed have fans on your tank. Maybe try to cram a few more in there. Other than that and the chiller option, you might try to raise the fixture further up off of your tank. I'm not sure if your canopy would allow this, but I know of a few reefers that built standoffs for their canopies (Doxyman, in particular, did a great job) so they could fit MH setups in canopies built for flourescents.
I'd definitely lay off any new additions, I got frag happy on my 7 and paid for it for a month or two afterward with nitrites that wouldn't go away. Also go easy on feeding.
I hear good things about the sea hares, but no personal experience with them. My lettuce nudi, RIP, was great at tearing up the hair algae. Mowed through it pretty quickly. Sadly, he also was partial to getting sucked into my HOB intake. The first two times he escaped death with varying degrees of mutilation. Third time, unfortunately, was the charm. If you get any sort of nudibranchs make sure your intakes are covered. Since your tank is pretty large, I might recommend you pick up a few.
Oh yeah, about the cloudy water, are you running carbon?