Caulerpa Verticillata maybe? If so, does anyone have tips on keeping it in check without it taking over (besides kill it)? It seems to be thriving even in brackish water.
Maybe Bryopsis. Verticillata appears to have end which are more fan like but there are so many variants of most algae it can be hard to be sure at all with photo id when it comes to stuff rarely seen in the hobby. More importantly though since you aren't concerned with eradication the best management method is the same for both is to simply pull it out by hand. The most effective tool for keeping algae under control imo is a refugium with a good light.