Since writing my prior post I have branched out and tried some new things with my seahorses.
I still keep the tank in the low 70's. My 56 gallon has rockwork, macro algae and coral that could potentially be trapped and eaten a day later, even with my strict maintenance practices. Cooler temperatures definitely helps slow down pathogenic bacteria growth.
I had minimalized the addition of fish for quite a while as I knew they can carry pathogens that the ponies do not have an immunity against. My seahorse tank was looking so inactive though (except at feeding time, haha), so I had decided to add some very quiet species of fish. Cardinal fish and blennies were my choices. My seahorse tank has a large open water area where I figured the cardinal fish would hover. I have a pair of pajamas and a pair of bangaii. I also have a lot of rockwork on the right side of the tank. The peppermint shrimp have had that area all to themselves until recently when I bought some blennies. The linear blenny enjoys the rockwork and is very entertaining. The yellow head striped blennies are mostly in the open water area now that they are comfortable. I QT all fish even though they were CB. Then when I added them to the tank I upped the WCs greatly to delute any pathogens they might be carrying. I will eventually go down to 30-35% a week after I feel the ponies have had a chance to adjust to the fish. I am about 50% a week now.
Let me state clearly that keeping a seahorse tank with coral, macro algae and fish is a risk! Your chances of success as a new seahorse keeper are much better if you keep a species only tank and cater specifically to your ponies' needs.