Metal buildup. Fix it with a sequestrant and balance your pH.

Probably something like copper (from algaecides or corroded fittings) or iron (from well water or old pipes). The metallic taste is usually dissolved metals, not harmful in small amounts, but annoying.

First, test your water: pH, alkalinity, and metals. If pH is low, it’s more corrosive and metals leach faster. Raise it to 7.4–7.6. Then add a metal sequestrant (like Metal Free or a chelating agent) — it binds the metals so they stay in solution and don’t stain or taste. Shock the pool if needed, but wait 24 hours after sequestrant.

Don’t just dump in more algaecide — that’s often copper-based and makes it worse. If you’re on a well, consider a pre-filter for fill water.

Your tongue is telling you your chemistry is off. Listen to it.