Realistic lighting in eevee

Hi guys, is there anyway i can make this scene more realistic? especially the lighting, it feels like missing something

This scene is rendered with light probes and reflection cubemaps, and i used a fading sky hdri for a night-ish enviroment

Let the main source of light cast shadows on the ground. (that is rotate the sun lamp around till u see shadows on the ground)

You might need to extend the water layer into the horizon.

I hope ambient occlusion is enabled.

But im pretty sure Cycles would give this a very nice look. - maybe you are trying to animate. if not. make it cycles!

the ambient occlusion was on, but i wasnt aware that the distance was way too low, now i turned it to higher and it looks much better,
however i wasnt able to make shadows more visible i think it is because the enviroment is too dim, how can you make shadows in dark enviroments?
i am not animating it but my model is way too high poly that it will take tens of hours to render in cycles. anyway thanks for the help!

Whats your light source? HDRI? still it should be casting shadows. Check if it does. if the light source is too weak, add a sun lamp to mimic where the sun is shining down. Make sure Cast shadow is on for sun lamp and the render settings.

the light source are both from hdri and 3 sun lamps near to each other and pointing where the hdri sun is shining to, there are also area lamps shining at the tank and the cast shadow are on in all the lamps