With such a small aquarium, you need to do a complete cleanup : RIP clean. Less than 2 hours work. Live rock with coral can be treated in a 10% solution of 3% h202 for 10 minutes, outside of tank. Remove all sand and flush with fresh water.
As a final thought, consider an Oxygenator system which uses hydrogen peroxide to manage system nuisance algae.
Will this kill/affect my decorative Macroalgae? I have 10+ species.
I did a complete clean of the tank (scrubbed all the rock and siphoned all the sand) within the last month. It all grew back. Last week I did hours of scrubbing and maintenance again. I don’t want to have to continually do hours and hours of scrubbing every week - if that’s the solution I suppose I can keep doing so but there must be some other solution?