I always shoot RAW...
I will most often use, in tricky white balance situations, a white balance target (I specifically use a WhiBal Card) and either set a custom white balance or balance my whites using the White Balance Eyedropper in Camera RAW. Or, I occasionally pick out what I guess is a neutral gray portion of the image and get my balance on that point using Camera RAW...
My question is how to get a correct (rather than just a pleasing) white balance when shooting into an aquarium tank. I shade my lens and camera using a rubber lens hood or other such device which usually does quite a good job of preventing reflections.
However, if I cannot include a white balance target and/or if there is no neutral gray area in the image what should I do? An example is this image....

I didn't really remember the colors in the above image. So, I just aimed at getting a pleasing white balance

BTW: the water within the tank was somewhat murky with lots of particulates floating around...
I can often guess at the white balance in an image like in the following even though it was shot through a Plexiglas enclosure and the light within the enclosure was strangely greenish
How about using one of these?
https://www.ebay.com/itm/ExpoDisc-EX...wAAOSw9hdaGFLq
Or a cheaper one like this which "might" get me within the "ballpark" as for white balance?
https://www.ebay.com//itm/Mennon-77-...UAAOSwG-1WyCDYadobe photoshop 7.0