For the record, there is no "cure" for algae as it's not a disease. That's the only reason the word "cure" is in the title.
Now for HOW to spot-treat algae! (More about "why" after the how...)
Depending on your confidence and where you need to use it, maybe wait to see how that first patch reacts over the course of a week before you decide how to proceed.
So why spot-treat?
In a nutshell: It's a very harsh treatment on the algae, but has almost no impact on the system's maturity or stability overall.
Contrast this with almost every other "algae treatment" you can name – most treat the whole tank vs just the algae. (I actually can't think of any other exceptions beside this right now. Hm.)
Now for HOW to spot-treat algae! (More about "why" after the how...)
- Fill a small syringe with 1-2 mL of regular hydrogen peroxide
- Shut off all flow and wait for the water to become totally still
- Treat a patch of algae at it's base – 1-2 square inches in size
- Wait a few minutes and and turn the systems's flow back on
- That patch will be toast
Depending on your confidence and where you need to use it, maybe wait to see how that first patch reacts over the course of a week before you decide how to proceed.
So why spot-treat?
In a nutshell: It's a very harsh treatment on the algae, but has almost no impact on the system's maturity or stability overall.
Contrast this with almost every other "algae treatment" you can name – most treat the whole tank vs just the algae. (I actually can't think of any other exceptions beside this right now. Hm.)