Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Yep, that's true. May cause other algae too, not just BBA.
For a single bottle, watch the drop checker. Some drop-off in level over time is normal. But when you see it start to drop faster, it's time to change it. Remember how many days it took. In the future, replace it one day before the drop would have started to accelerate.
If you have two or more bottles, replaced on a rotating basis, you can time things so that a single bottle at a time is allowed to burn completely out; because other bottles are taking up the slack. Less waste.