Omg please no!
I'm sorry but seahorses and octos will NOT do as tankmates! Seahorses have VERY specific requirements and need to be kept in a species tank, not added to a tank set up for another animal. Just as with with an octopus these requirements must be met exactly or your seahorses will not survive. Seahorses are also very succeptable to stress. Even if the octo didn't consider the seahorse a food source, if it were to grab onto the seahorse it could easily injure and stress to the point of death. They're very delicate compared to other types of fish. They are also very slow and wouldn't be able to escape if they felt they were in danger. Many seahorses have died as the result of a hitchhiker crab that snuck it's way into the tank and decided to take a pinch at a tail. That results in stress, injury, infection and death in some cases. Imagine what a curious octo could do.
I can see how some of you may have been lucky with some of the larger species of seahorses like pots, but that's just what it is...luck. Keeping a seahorse with an octopus would be like keeping an octo with a trigger.
74 is ok for SOME seahorses. There are 3 different temperature ranges that seahorses are found in.
Remember these are min and max temps...the coldest temp they can survive at doesn't mean it's a good idea to keep them there.
1) Tropical species - kept at 74-78 degrees F (24-26 degrees C)
2) Subtropical species - kept at 70-74 degrees F (22-25 degrees C)
3) Temperate species - kept at 66-72 degrees F (19-22 degrees C)
Brett please reconsider this idea...especially now that CITIES is in effect seahorses are extremely hard to come by in the US right now and they're also very expensive. If you can afford to buy the seahorses and provide for them anyways, think about setting up a tank just for them. In the end it will be much better for all involved. You also mentioned pipefish. They have even more specific requirements and are much harder to keep than the already hard to keep seahorses.
Check out www.seahorse.org
if you have any questions about seahorses.
I apologize for coming across so strongly. I just wanted to make sure that everyone who thought this might be a good idea, knew about the special requirements that seahorses need to survive. It would be really great if it were possible. To have 2 of the coolest creatures in the ocean together in a tank would be amazing...but it just won't work out. Again I'm sorry if I offended anyone, I'm just passionate about seahorses as I'm sure a lot of you are about octos.