U have a chiller. Why don't you lower the temp slowly?
1 degree a week.
Right now 78 is above max.
Most people would keep seahorse tanks around 73-74.
Check out seahorse.org
That's pretty much what they do. Just hang. Etc.
As long as theyre eating. All is well.
Thanx
-Joe
That sux man, sorry for the loss
That's what gonna happen when you keep them at 78 F...
You should read more before you try to keep seahorses;
http://www.seahorse.org/library/articles/SeahorseFactsAndInfo.pdf
Also check this about has bubble disease.
http://www.seahorse.org/library/articles/GBD.shtml