EDIT - Thanks to Cortez Cardinal and the creator Silent aka CookiePLMonster, here's the link[cookieplmonster.github.io] to an unofficial patch which fixes all those mouse problems this game has on newer systems plus an interesting read how these things were fixed:

Originally posted by Cortez Cardinal on 21 Apr @ 7:11pm:

No need to fiddle with anything anymore!

Just use the SilentPatch[cookieplmonster.github.io]

Obviously, after installing the patch, the following steps aren't really necessary anymore, but I will leave the guide as it was nonetheless since... well, since I can. ;P

Aquanox, being an older game, nowadays has huge problems handling modern gaming mice and their to back then comparatively high polling rates and DPI, resulting in the latter being nearly or sometimes even being completely unresponsive. Unfortunately, there's no real way to really fix this issue but to play the game with an older mouse, there are however some workarounds that make this atmospheric deepsea spacesim atleast playable again without having to dust off and fall back on ye olde ball mouse.

Adjusting mouse settings

To combat aforementioned issues, you'll have to manually adjust your mouse's polling rate and DPI. Most gaming mice are delivered with the ability to do so in their driver settings or some special configuration software, e.g. for Logitech devices this would be SetPoint or their newer Logitech Gaming Software. They also provide the feature to create profiles for specific software, so that you don't have to go through the hassle and change it back and back again every time you want to roam the deep seas.

• Lower your mouse polling rate to 200 Hz*.
  
• Lower your DPI settings also to 200.

*Or lower, everything above this value might also work to an extent, but will leave some room for input drops.

If you unfortunately do not have such an option available, there's also the alternative to try to adjust it via Windows' own Control Panel -> Hardware and Sound -> Mouse and then selecting an adequate Pointer Speed under the Pointer Options tab (just play a bit with the slider, the lower the better).

Fiddling with Aquanox' configuration

There are also two things reportedly helping with fixing the input loss that can be done by tweaking the game itself. None of these require you to adjust the ingame mouse sensitivity, but in some cases it might also help to do so.

1) Open your Windows Explorer, find "steamapps\common\Aquanox\ini\ctrlsp.des" and open it with NotePad or something similar.

2) Search for the following values (CTRL+F):


Change them from -0.322222 / 0.322222 to something like -0.022222 / 0.022222.

3) Deactivate VSync in the ingame options.