Omni pH Decreaser
Omni pH Decreaser is our favorite pH reducing product, perfect for spring and summer, to help prevent or clean up string algae blooms. This granular chemical is designed to slowly lower the pH of your pool/pond water and is safer than liquid acids like muriatic (hydrochloric) or sulfuric acids. Slowly lowering a natural pool's pH is better than making any sudden water changes, which can harm your plants, beneficial bacteria and fish.
For dealing with a string algae bloom; first pull out all the string algae you can, either by hand or with a net or pond vacuum (it's wonderful for composting), then lightly sprinkle the recommended dosage for your NSP (based on gallon size) directly on the algae that is attached to rock surfaces/wood walls. The offending algae will die and look “dusty”. Give the surfaces a gentle scrub if needed to loosen the dead algae, then use a pond vacuum or net to remove the larger pieces. Smaller bits of dead algae should filter out through the skimmer within a day or so.