I feel bad had to go out and get more parts it wasn’t the air pump always use them even in bigger up to 10 gallons this is only 5 gal. Anyway , main thing here is water looks to low, I screwed up too when I left it unwatered for few days got junky quick, make sure levels are touching the bottom of net pots. Use algaecide if anything or let me know I can have some sent to u but they should have it at local pet store. For now , dump and change and refill water, with small amount of nutrients.
Algae can build up from few things need more water and best way to prevent is cover whichever holes you are not using to grow in. Will cause algae