What camera do you use and what post-processing do you do? I have been using superb free program called darktable to improve images sharpness and colour etc.
I use an iPhone se with a reefin art lens kit. I use the orange lens and full blue lighting. Coral has to be close to the camera, this acan was near the front glass.
I put the camera straight up the the glass and click to focus on the coral, it will be blurry. Then very slowly I back the camera away little by little until it is sharp and in focus. Then I zoom until the polyp is full screen on my phone and take the pic.
I don’t do any editing or processing.
I used same method here on this goni
And on this riccordea I did same thing but more/less zoom
And this torch is much farther away. I just put phone up to the glass and clicked the coral to focus on it, then zoomed in and took pic
Make sure the glass is clean and turnoff all water pumps/flow at least 10 min in advance so the object isn’t moving