Even after these decades I know zip about plenums and his other ideas on that. BUT! What I agree with here 100% is that phosphates are our enemy. I say big water changes and constant filter cleaning will do it...but all my life when I read of natural waterways destroyed? Its phosphates...runoff from farms and factories. All others are secondary pollutants..metals,nitrates..or exotic things. Yet,numero uno is always phosphates.