A UV will do next to nothing to remove the risk. UV's only kill what pass through them. Bacteria's grow very fast. Some can double there population in 20 minutes. A UV is great if using a central sump to keep multiple tanks from sharing pathogens, but will not eliminate the bacteria population in a system.
Temperature really is the issue here. At higher temperatures the bacteria's are much more virulent and will change there protein structure to one that is not recognized by the seahorses immune system.
Even with previous resistance (an asymptomatic carrier state does appear to exist) to the bacteria, at the higher temperature the population density of the bacteria coupled with it's aggressive state is a much larger danger then a tank with a lower temperature.
Reef tanks are fine at higher temps, seahorses used to be considered to have similiar needs. Those of us that have followed seahorses for some time, and have kept them succsessfully have seen how much of a difference the lower temps make in regards to disease control. When I started in this hobby a seahorses would live for a year or two tops. When I kept an adult WC for 5.5 years I was kind shocked, Davd kept one for 7 years. Just saying things are moving up.
Oh, and the clown and chromis would have to go, the hairy mushroom is iffy, the shrimp staying would depend on species of the shrimp, and the seahorses will pretty much kill your acro with it's constant hitching.
My advice would be to turn our 30g into a seahorse tank when you move up to the 75g. Get some macro algae and branch rock for decor. The macro will help with the water quaility, provide a place for the seahorses to play, and give you a new challenge in the hobby.
JMO, that and a quarter will still get you a phone call, some places.
