Water changes are key..........as you have already seen. Make sure you check your nutrient export and that Nitrates and Phosphates are as low as you can get them (0 is preferred). But for removing it directly, I use a 3/8" vinyl tube connected to a 3/8" rigid tube and siphon out what you can see during the water changes. The rigid tube lets you get right in there all pull it off the rocks and out of your tank.
If it is stringy , it's probably Dino's. From what I have read ... Water changes will make the situation worse. I had Dino's and didn't do water changes and used hydrogen peroxide to kill mine off . During the peroxide dosing , I used a very short light period for a couple of days .