An apparatus may mount an in-stream, continuous contact, visible, sacrificial anode in a fluid passage for the electrolytic corrosion protection. The apparatus may function to protect heat exchangers and/or other metallically connected system components that share contact with electrolytically active fluids. The apparatus may consist of an in-line anode cartridge including 10 a collar body and a viewing port. The apparatus may include a site glass and compression fittings which seals the device causing corrosive fluids to flow past a sacrificial anode. The apparatus may include a visual indicator and an elastically compressed member (e.g., spring) which facilitate continuous metallic/electrical contact and inspection of the anode through the viewing port without system shut down or disassembly. The elastically compressed member 15 and gauge assembly fills the view-ports with a bright indicator as the anode dissolves and the elastically compressed member expands. The apparatus improves inspection, replacement and effectiveness of sacrificial anodes in electrolytically corrosive environments.