When I had my big horses, I had a constant problem with bubble which is a bacteria problem. I did frequent water changes. I only had 2 in a 20 gallon with a 10 gallon fuge so talking from my experience. Bacteria infections were the most discussed problem on the seahorse forum.I’ve been hearing that old crap about number of seahorses in a tank ever since I started on both of these sites back in December truth of the matter is Seahorse are a community fish, they like to hang together for safety as far as needing a tall tank so they can swim up and down also crap,maybe it’s just my horses but it seems to me they spend 99% of their time down low at the bottom And the number of horses in a tank thing is all about poop it’s just people that don’t want to keep up on their maintenance religiously for the comfort of the horses. (Oh by way just my opinion)
I think you are the unusual and lucky one because of the access to real Ocean water. (and if I had a bigger tank I would take you up on the ponies and ocean water ) The breeding farm in Hawaii has their facility linked directly to the ocean.
The height is mainly because they like to swim up and down while mating. Mine was 20 xhigh tank and they used to go all over the tank...top and bottom. By the way, the dwarfs stay mostly on the bottom too.
The one big girl I had used to dance to get my attention to feed her I do miss the bigger seahorses.