The short answer
Lower phosphate the same way you handle most nutrient problems: reduce the input and export the excess. Feed less, remove waste and dead plant matter, do regular water changes, and — if it’s still high — run a phosphate-removing media in your filter. Phosphate isn’t toxic to fish at normal levels; the reason to control it is that it’s algae fuel. Tackle the source first and the reactive media second.
Cut the source
Most phosphate comes from food and waste, so overfeeding is usually the root cause. Feed smaller amounts, remove uneaten food, trim decaying leaves and vacuum the substrate during a water change. Some tap water is also high in phosphate — test yours with a liquid test kit, and if it’s the culprit, cutting it with RO water helps (see using RO water).
Export what’s already there
Water changes are the simplest export route — they dilute phosphate along with nitrate and other waste. For stubborn cases, add a phosphate-removing resin (like a GFO or iron-based media) to your filter; it binds phosphate until exhausted, then you replace it. Browse options in the filters hub.
The bigger picture
Phosphate rarely acts alone — algae blooms usually need excess nutrients and excess light. Balance both. See safe nitrate levels, and if you’re battling algae, our answers on green water and algae on glass go deeper. More in the water testing hub.