Recently I have discovered the pipe to my radiator is looking a bit weird. From what I can tell, it does not quite look like corrosion, neither like mold. I think I recall there was some green paint on the pipe, but I am not sure. Neither would I know how it would turn into this. Any ideas what this could be?

Picture of the pipe


You're seeing corrosion salts forming. In the presence of a water leak, copper will display greenish or bluish crust as the corrosion mineral in the water reacts and dries. Blue-green is copper sulfate, green is copper chloride/oxide. Fix the leak.

Discuss with your HVAC expert to find if you need to demineralize/deacidify the water in your heating system.

This is heated pipe, cold water pipes can show a greenish tinge where a lot of condensation from damp air coming in contact with the pipes condenses and drips off the copper pipe.

  • Would that have flakes on the floor and on the pipe? I thought corrosion was more on the metal itself. – Florian Mayer Oct 10 '15 at 21:07
  • Yep, Algae is slimy, you'd have stringy stuff, corrosion is crusty and flaky and bumping the dry portions will leave flakes and powder on the floor. It's the copper form of iron rust. What you see is accumulating from water evaporation of a solution on the outside of the metal pipe. – Fiasco Labs Oct 10 '15 at 21:11

It's algae, looks like you have a leak. Algae needs a lot of water and sunlight to survive. You can kill it by cutting off either of those two elements. Then again, you could let it live, give it a name and have pet algae instead.

What is this? A biology test?

You can prove its algae by getting a dish of water, putting it on a window sill, putting some rocks in and then adding the green stuff to the rocks. If it grows, its algae.

  • Hm, are you sure it looks like algae? I do not think it is getting lots of sunlight where it is, to be honest. The curtains are closed most of the time and it is on the floor right under the window, where the sun is rarely at a level that they would get any direct sunlight. – Florian Mayer Oct 10 '15 at 19:08
  • It is getting sunlight somehow. I guarantee you that the green stuff in the picture is algae. I know it well. – Tyler Durden Oct 10 '15 at 19:17
  • If it is wet or most likely slimy to a degree, algae it will be.... The cast off drips on the floor are a curiosity. I have seen pipes corrode to a bad degree, but the green caused by corrosion is a lot more like a turquoise color. – Jack Oct 10 '15 at 21:02

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