Planted Tank is great for planted aquariums, and Fish Lore has an active general fishkeeping forum.
Vortex is a Volkswagen forum but has tons of conversation around other brands, too.
The official LOTRO forums are the only official game forums I've found that aren't super toxic. Great community.
Really, I think old-school forums are best for specific niche interests.
That said, I'd probably be happier if I wasn't living in a basement with a single window.