yeah I was going to say you can see a few of the mangroves wilting in the earlier picture. Did you acclimate them? Trees should be acclimated to reduce stress, but that is how plants can be sometimes anyway. Good thing you have some extras there it looks like. Seahorse safe inverts are harder to come by....they have a tendency to outcompete for food, or be on the dinner plate if they are very small shrimp. Your best bet might be for some sessile inverts, dusters, gorgs etc...if you go the seahorse route. The "org" has lists of what you can keep with horses without trouble.