Post a sample picture and we can tell you what you would need to do to fix it.
But basic manual macro settings are...
Use a tripod.
Turn off pumps, let tank sit for 5 minutes and settle before you start.
Set ISO relatively low, only as high as you can get it without introducing digital noise.
Set the aperture to wahtever you want. If you want a really isolated subject, do f/2.8. If you want lots of the picture in focus, do f/11 or higher although you can start using quality getting lots higher.
Then just adjust your shutter speed to expose your shot correctly. Since you're using a tripod you can get pretty slow shutter speed and get away with it.