More plants doesn’t have to cost much, you can start off with just a few bits and they’ll quickly populate in a few months
As a minimum I’d say some floating (water lettuce, salvinia), planted (java fern the windelov type looks better imo, sagittaria subulata as a longer ground cover), mosses like java moss and Christmas moss
Keep the lighting on for ages to promote algae growth on the wood and glass, shrimp love to graze on it and what grows on it
Something different like marimo balls, again shrimp love what grow on it
Get some snails, Malaysian trumpets would be my choice, they clean up good and are interesting to watch in their own right
Mythicalteameat 
Add actual real living plants and more hiding spaces. Also take out the plastic plant
More plants doesn’t have to cost much, you can start off with just a few bits and they’ll quickly populate in a few months
As a minimum I’d say some floating (water lettuce, salvinia), planted (java fern the windelov type looks better imo, sagittaria subulata as a longer ground cover), mosses like java moss and Christmas moss
Keep the lighting on for ages to promote algae growth on the wood and glass, shrimp love to graze on it and what grows on it
Something different like marimo balls, again shrimp love what grow on it
Get some snails, Malaysian trumpets would be my choice, they clean up good and are interesting to watch in their own right