I'd like to incorporate my seahorse tank into the main system, so that they share the same water. Two issues: cooler temperatures and lower salinity seem to be their preference. I've not quite figured out how to make both work well enough on their own to pull it off.
It would be nice if I had a very slow return going up to the seahorse tank that turns it over maybe 2x per hour, and a fan blowing down on the surface to cool it sufficiently. That might work, but I may end up having to heat the tank all night as the fan overcools it.
The salinity thing is tougher. I'd need a little RO/DI water added to lower it before it enters the tank, but not too much.
My goal seems to be getting more and more toward one community system instead of all these separate tanks to care for.