Hot water from airstones? Ah you mean your airpump is getting hot &-or blowing hot air straight into your Res/tanks/buckets? I find using a dedicated fan on the pumps intake helps keep the pump cool & cool airflow into res/buckets. Some pumps get really hot, especially after airstones have been swamped/strangled by root mass. Nice trick that really works well for me! sorry if i missed the point. Any pic updates etc!
G'Luck!
G'Luck!