I really like the options for fish the most, there are room for improvements but overall it's a great game to use for tank design ideas/test runs before doing them in real life.
What I enjoy:
The options for fish between species, colors, and variations
The plants options!
Many different tank sizes and styles
Accurate fish info
The music is 10/10
Great graphics

What I would personally like to see:
The mosses need more dark texture; they're all the same green shade and it's too bright
The corydoras should hang out closer to the bottom more, they hover too high up
The fish do not school (tetras, corys, etc), which is a little sad to see considering the info showing they're social; it'd be cool to see the social preference executed
Add shrimp and snails for a little extra fun!
More wood options would be very appreciated
Dark black substrate without the colorful rocks
Being able to pan the camera upward when zoomed in
An undo option when you accidentally move an object