salt water is a big learning curve
the theory may be spoton
but practical is another kettle of fish
i have been keeping and breeding seahorses for 25 years
the tank maybe 250 litres but the surface area isn't large
you are right they do need height, for breeding only
they need clean water
they are not a fish to start keeping marines with
waterfaller wasa trying to be helpful
and starting out keeping marines is better if you have experienced hands to fall back on,
when the problem you come across is not on the internet or in a book
you need to know it back to front, inside out and upside downside
good luck