Yep. Bacteria in liverock esp the denitrifying bacteria will definitely die off if they come into contact with the atmosphere. You denitrifying bacteria population will have to be re-established all over again.
Did'nt notice the bracing until jdn pointed it out. I would be cautious in filling the tank to the brim especially with such a thin middle bracing.
The design of your sump is wrong as water should only be allowed to flow over the DSB and not right through it. Anyway, why do you need a DSB in a FW setup? Frequent water changes and maybe the use of freshwater plants will easily remove any nitrates.
I don't think it would as the water flow through it is quite gentle and the fluidized reactor is not pressurized. Some small particles do escape into the sump initially during the tuning. But once you get the water flow in just right it would'nt be a problem anymore. For the activated carbon chamber I only fill it about 1/3 full. With the water flow adjusted the smallest particles only reach 50-60% of the chamber height. The rowaphos (500g) only occupies less than 1/10th of the height of the chamber. Smallest particles reach only 60-70% of the height of the chamber before falling again.
Hope the sea turtle hatchlings belong to more common species like olive ridleys etc. If from species like hawksbill and the more endangered kind then..
Can consider T5s too. You'll save in the long run in electicity bills, heat generated and the cost for replacement bulbds. T5s can last anytime between 1.5-2 years with only a minimal drop in optimum performance.
I used to have a maroon. Single, unpaired. Bought it as a bright orange individual, after 5 years it was a dull brownish-red individual. Did'nt have efficient protein skimming back then.