I agree there is not much in 682 that addresses these tanks.
If it is not 682, it is not addressed in the code at all and they are invisible to the inspector. You only have the GFCI requirement for "outdoors"
682.1 Scope.
This article applies to the installation of electrical wiring for, and equipment in and adjacent to, natural or artificially made bodies of water not covered by other articles in this Code, such as but not limited to aeration ponds, fish farm ponds, storm retention basins, treatment ponds, irrigation (channels) facilities.
