For sure the indicator is when the orange flesh has crept back over the top of areas it's receded from, that's how we know it is healed. Unable to tell currently not long enough. The only indicator you need is visual proof that frozen feed you have is going into the polyp. If it is, you will succeed.
In nature, that orange spreads onto other rock, thats when growth is ideal. In the meantime simply plate it back across where it receded.
In my reefbowl it would take about a year or slightly more, and that's with exceptional weekly feeding directly when the polyps are out not just placing feed near the coral. Use teaser feeding
Tiny bit wait 30 mins should bring out polyps
Then you use a turkey baster injector syringe to squirt blenderized mysis not whole ones
Mix in rods feed
Inject that into each open polyp after coaxing them w pre feed smell
Injecting into open polyps is less tank waste will take months and months to fully recover, 100% chance of recovery.
if you are serious about saving it then you have a full ability to do it. Simple export work on your main tank, far more work than before the attempt since basic tank feeding won't regenerate it...allows you to spot feed the coral well enough to recover. It's non photosynthetic
Only heterotrophic feeding repairs it, it's been in negative nitrogen state for a year clearly, barely accessing water borne whole feeds often enough to preserve life. For sure I would have that reproducing in 15 mos total orange coverage
One of the best tubastrea references, sexual not asexual reproduction induced, is pj reefs 2.5 gallon pico of the month from nano-reef.com maybe two years ago roughly, search. By adding live cultured phytoplankton to the other food offerings he was able to get the coral to reproduce in a way highly uncommon to all reef tanks with this genus. Most repro is overgrowth type although several online refs exist for gamete based reproduction...this was the first in a pico reef
Creative feeders have taken the coral out nightly, coaxed it to feed, feed in a still bowl of sw, leave in 2-3 hrs
Rinse out back in tank. Moving coral from bowl to tank is harmless and nicer than the tide. Brings fresh brine or mysis into every polyp outstretched.
Creativity but they all revolve around feed and export. Feed it nightly if serious about regeneration it's guaranteed to work. Casting feed into the tank won't help it, only visually verified uptake into the polyp, positive nitrogen counterbalance. After fix, perhaps stronger cast feeding might sustain it, just not during repair time.
