Alk quitre high and likely causing the stress which is what this frag is showing. These coral also do best at lower third of tank level where there is moderate light and water flow. One of the more important requirements for frogspawn is Placement. It is an overlooked element that contributes to the overall acclimation and sustainability of your frogspawn.
Frogspawn Corals do best when provided a moderate amount of lighting, with many hobbyists finding success with an added bit, or partial, shading. Euphyllia (theyre a member of this group) do not enjoy direct high lighting. Keep in mind that the amount of lighting and the degree of water flow work hand-in-hand in sustaining healthy coral life and growth. Although technically capable of survival, Frogspawn DO NOT appreciate high or even moderately high flow. They will open much bigger in gentle flow, and will be able to grow into those beautiful serene tendrils that you see swaying within your habitat. (see my pic below- this was a size of a quarter a year ago and now 6"x4")
I cannot overemphasize the incredible importance of both lighting as well as placement. Never, ever haphazardly place your corals, select your lighting, or randomly pair different specimens or species within a tank, and just hope for the best. Remember, like any coral, Frogspawn Coral requires a very specific amount of lighting, and in this case, it’s not a whole lot. Unlike many other corals, Frogspawn Corals don’t require a whole lot of lighting. They are also 100 PAR, but even levels as low as 50 PAR will work well for this beautiful species.
Frogspawn are not the most aggressive eaters. Broadcast feeding is typically the easiest, most effective approach. Additionally, if there is too great a flow, or if there are fish in your habitat that are aggressively harassing them, they’re just not going to eat. Even if they are able to successfully get the food into their mouths, they often quickly spit it back out--quick enough where they may not even be digesting any of the food.
Lastly, they do shrink like as shown in your pic in the evening.
here's a pic of some of mine: