You know with temps getting high and if you cannot maintain a cool temp, you can run a reverse phytoperiod. Run the lights at night when it's not as warm. It sucks because unless you're a night owl, you won't be able to enjoy it as much, but it keeps things stable. =) I read where you wanted to add a Cuke. At least that is what I think you meant. Don't add one. =) They should only be added to larger tanks. That tank would most likely be too small for one. They will not eat prepared food either. You can also get a fan from walmart, I got one for 10.00 and blow it across the surface of your tank water. Evap cooling. Really works. If you decide to go with a sump, they are really nice because you can point the large fan across the water in the sump.
I think it might be a little hard to include a sump with that beautiful nano though. Have you seen people do it? You could still add a little sand to the tank if you don't like the look. A little sand will not be harmful. A DSB though would most likely crash in the future. If you go to the Marine Depot website, search their forums. I asked Dr. Ron Shimek the same question about my tank. I wanted a DSB in the tank and the refugium. He said it would most likely crash. My total water volume is 65 gallons. Some people have said though, to take what he says with a grain of salt. =/ It's all about research. Research has helped me quite a bit.
Also, are you looking at Reef Crystals at your LFS? All the salt mixes will be more there. If you go to
www.drsfosterandsmith.com they usually have good prices on their salt. I get the 160 gallon mix and I've always caught sales. It's much cheaper I have found there than in my LFS. Check it out. =) Love your tank. I love those blue clove polyps too.