Do you have a Drop Checker (DC) if so what colour does it change when CO2 is on ?
Also how long before lights on is CO2 coming on?
Plus what light do you have? Is it dimmable or can you rise the height of the light? Or floating plants may help
Most Cladophora sp. does clearly grow in branches it's more plantlike and feels hard and gritty and you feel it snap when it breaks. I guess it's an evolutionary step toward Chara which is an even more plantlike alga. If you look at it under high magnification it looks more like a flat leaf structure than a strain built from single cells connected. Like mini Chara.