Solomani Navy: Armaments and Pop-Up Torpedo Barbettes
You can reload them, but you should consider how that could be accomplished. Let's ignore costs, which would be even more speculative than tonnages.
1. First, you lock the barbette into position.
2. A hatch pops up at an angle behind the barbette; your ship just gained three tonnes in volume.
3. The torpedo reloads slide out of the hatch and into the barbette.
4. The hatch pops shut and the barbette is released.
For that operation you should allocate six tonnes for the reloading hatch; you could allocate more tonnage for a torpedo magazine.
You could have reloading done directly underneath the barbette, but unless you allocate a lot more space, the torpedoes have to lifted vertically into the brbette, and I'm fairly sure that the turntable would force the launchers to be spread wider apart, and the reloading mechanisms would have to be split.
I'm not sure how much the designers were inspired by real life, but you could have upto five torpedo tubes connected, though I'm sure that there's nothing preventing the creation of a barbette small enough to hold only one torpedo, though suspect you want to have a reloading mechanism beneath that.
One variant, if you don't mind a rather prominent kinetic sculpture sitting on top of your ship:
That would make it possible for a vertical reloading.
Personally, I rather go with submarine variant torpedo launches, but let's assume that target acquisition is more faster and more accurate this way.