It really is beautiful, Dawn. It's so sad to hear about Boaz. Did you find out what the issue was? An unbalance inside of him?
I have to admit that I am only guessing on all of it, Nick. I think I can feel fairly sure that the return pump not running was definitely a contributing factor. Without the return the tank was aerated but not much filtering other than biological from the LR. Still with only 3 ponies and a royal gramma in almost 60 gallons of water they should have been alright for the 4 days I was gone. So my best guess is when I got the text that something was wrong, the macros in the fuge were already in poor shape and disintegrating. Then when I instructed my fish sitter to add ro/di water the sump pumped dying macro algae matter into the display just long enough to pollute it. Then the level dropped again which stopped the skimming from reaching the display thus destabilizing the tank. Most marine fish and corals would have weathered that ok but seahorses, (especially the males) do not handle a high amount of organic matter in the water column. It probably did not help that the salinity dropped fast too.
I have read that it is theorized that it creates an inbalance in their system and that is what is believed to cause gas bubble disease, which is what Boaz has. (GBD is nearly always fatal although it can sometimes be treated with Diamox. Diamox is a medication used for glaucoma in people so it is not easy to get since it requires a prescription.) I don't really understand it all about high organics but I know that is why experienced keepers recommend such big skimmers for seahorses. That is the same condition that killed Adam, my first male seahorse. I am going to ask my vet for a script for Diamox and research its shelf life and price.
I hope I did not overwhelm you with too much info Nick but if someday you keep seahorses, you should be aware of this stuff.