I’m impressed with your proposed setup for your Zulu-lulus (Hippocampus capensis), sir! With the efficient filtration provided by your Emperor 400 and nano protein skimmer and the cool water temperatures you are achieving, Zulu should thrive in such a setup.
In my experience, Zulu-lulus (Ocean Rider’s strain of captive-bred-and-raised H. capensis) do well at temperatures in the 72°F-75°F range. As long as you avoid temperature spikes above 75°F, it isn’t really necessary to maintain water temperatures in the sub-70°F range as you would for wild H. capensis. Set your water temperature to hold at 72°F and the domesticated Zulu-lulus should thrive. That’s an excellent compromise temperature for them — cool enough to keep them comfortable and avoid any problems with heat stress, yet warm enough to bring out their best colors and increased activity levels. So I would strive for stable temperatures around 72°F.
If you search the discussions on this forum for the key words "Hippocampus capensis," you will find a lot of additional information on the care and keeping of Zulu-lulus that you should find interesting.
Best of luck with your new Zulu-lulus tank, Bryan!