I specialize in small electronics repair, it sure to be my job, now it's a side gig. If it's water damage,
sometimes just cleaning the corrosion off any contacts can get you going. However, often times the corrosion has shorted components out and things can get complicated. Depending on components used, most can be replaced or substitutes used of the faulty component is identified.
I've never worked on aquarium lighting but I've worked on an absurd amount of water damages game consoles....same thing right?
Let me know if you need another set of eyes on it.