Great thread and a great shallow one you got there! I was thinking of doing the exact same setup! I have 5 seedlings right now; one in the sump, one in the display and 3 in the overflow temporarily (long temporarily :oops:).
I've had my mangies since December, red mangroves Rhizpora Mangle. Got them off ebay :D
At first, they were very slow to show any growth, but then I started spraying them with RO water at least once a day and BAM amazing growth! Maybe you should try that!
Also temperatures here in Egypt have been soaring all summer, ambient is around 30-32 degrees C and water temperature aroung 28-29 degrees C (sorry, no fehrenheit:D) , which is too hot for comfort I know! But no chiller and no AC :confused: Also somewhat humid as I live in a coastal city. Maybe this weather helps them feel at home?
We do have natural mangrove forests here in Egypt (although a different species I think) and they live in super hot areas near the southern end on the Red Sea where day temperatures can reach near 40 degrees C or more with blasting sun all year round.
Keep up the great work and inspire us! I hope I helped:)
All the best!