Haven't used these ones personally but these are one of the cheapest with good reviewshttps://www.amazon.com/COODIA-Internal-Aquarium-Submersible-Disinfection/dp/B07V26V5MS/ref=sr_1_5?crid=14NURUQBSLK94&keywords=aquarium+uv+filter&qid=1683065168&sprefix=aquarium+uv+filter%2Caps%2C161&sr=8-5

https://www.amazon.com/AquaMiracle-Aquarium-Aquariums-Direction-Adjustable/dp/B0BFGV2Y6Q/ref=sr_1_10?crid=14NURUQBSLK94&keywords=aquarium+uv+filter&qid=1683065168&sprefix=aquarium+uv+filter%2Caps%2C161&sr=8-10

uv filters are pretty good even without green water algae, as it can really reduce outbreaks of open water bacteria that can infect fish if you have an outbreak when introducing new fish or plants etc

if you don't want to spend money, reducing light overall or doing a blackout over a period of time can reduce algae is well!