Did you shoot pictures in RAW format when you took pictures with your old camera without strobes? If so, you have a little more margin to recover light.
For your future pictures, make sure to:
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use RAW file format
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take a grey WB card underwater to be able to set the WB at the depth/time where you want to take natural light pictures.
To get the most WB adjustments, you'll need to process your RAW files in post processing. So to get the WB, take a shot of the WB card, that you will use in post-processing to adjust the colors.
So in post processing (Camera RAW), you use this WB picture to get the Hue/Saturation parameters, you can then apply these parameters to all natural light RAW files taken at the same depth/time.
To process WB a bit further, there are options a bit more efficient than tweaking the HSL sliders individually, that you can apply once you have imported your white balanced RAW files in Photoshop
Copy your picture in 3 new layers, then apply to each of these layers the following adjustments: AutoTone, AutoColor, "Match Color +neutralize option".
Each of these options do some kind of color/tone correction, "optimizing" the color settings of the picture.
Depending on the picture, one of these options will give better results than the others, so hide the others and work with the best option. These auto settings are often too strong, the next step is to smoothen the effect by adjusting the transparency of the layer.