How to take away the reflection on the fishtank?

I'm shooting photos of splashing fruit and am dropping them into the tank. I'm using a nikon d700 with 70-300 lens and I keep getting a reflection every time I take a shot. I just wanna get a solid black background which does not happen. Any suggestions?

This has to do with the flash on the screen. Put the lens as close to the glass as possible.

Put your camera on the inside of the tank.

Or just turn off your flash, turn up the ambient lighting so that you can rely on a faster shutter speed.

Two solutions.

1) Use a polarising filter.
2) Use a rubber lens hood to place the lens up against the glass.

Use a polarising filter

Point your flash straight up.
If you aren't using flash then there's a light source directly hitting the tank that you need to cover.

A more simple answer would be to not use a flash. Use flood lights of the same wattage.

A polarizing filter might help but the intensity of a flash is quite big so you might not be able to eliminate the reflection.

A better alternative is shooting from above in order to avoid photographing the tank.

Do both (use constant lighting or bounce your flash)… And use a polarizer.