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