what size tank, tank mates (fish and coral - some corals sting)
what species seahorse?
s.g. ammonia, nitrates, ph, temp (often seahorse do well a little cooler 74-76)
they are quite sensitive to water issues, but also feeding is tricky, they have short guts and need to be fed mysis gut loaded or soaked in stuff with omegas/fats/vitamins 3-4 times a day as they can die from poor nutrition.
the wild caught if a little stressed may succumb to disease as well.
when stressed they go pale like you describe.
feeding the babies if a newly born often needs to be every few hours to keep up their nutrition - been a while but i used phyto gut loaded rotifers and brine gut loaded with rotifers for mid age, and Piscine mysis and or hikari mysis as a source for adults.
I had one die on me (years ago) with perfect tank parameters and the other 4 were fine long term, necropsy i found a renal abscess and i cultured it (im a geek) and found vibrio - they were wild caught.
Hope your others do well
in future consider captive bred; i recommend seahorsesavvy.com as a possiblity