Were there other ballast tanks?

Yes, there were other specialty tanks including the bow buoyancy tank, the safety tank and the negative tank.

The bow buoyancy tank was also outside the pressure hull and was flooded along with the main ballast tanks. It provided added lift when surfacing and added downward momentum when diving since it was located just behind the bow.

The safety tank was inside the pressure hull and held about as much water as the conning tower. It was normally full of water. Should the conning tower be seriously damaged and flooded, the safety tank could be blown dry to get the boat close to neutral trim again. It was also be used to offset flooding elsewhere in the boat. The safety tank was rarely blown dry.

The negative tank was also inside the pressure hull. It was used routinely to submerge more quickly. This tank was located forward of amidships and was full when the boat was on the surface. It helped the crew submerge the boat quickly by providing the additional weight forward, pulling the bow down. It was normally blown dry as they reached periscope depth. It could also be flooded to get deeper quickly, typically from periscope depth, in case of an emergency. It would be blown dry again once the boat was at a safe depth. With this tank, the crew usually did not have to race toward the bow when submerging as the German sailors often did, as seen in the movies.