I believe if you check the amount of phosphorous content (< 0.01%) you'll see that at our recommended dosing this would only add 0.0005 mg/L (ppm) of phosphate to the water. This is completely negligible and poses absolutely no risk of algae growth. So unless you are planning on a 1,000 fold overdose you don't have to worry about ever getting any measurable phosphate from using Flourish. We don't sell Flourish as a macro element supplement which is why the phosphorous, nitrogen and potassium levels are as low as they are.
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