I am trying to set up an ore purification system to create metals (Aluminium,Copper, Iron, and Gold), Lithium, Flourite, and Hydroflouric Acid. I have all the Ore Purifiers, Arc Furnaces, Metal Smelters, Chemical Plants, and Assemblers all set up. There is a bug in the pipe connections that prevents me from placing the final pipe for the clean water line. All fluids except for water will make a complete connection; all clean water pipes will connect to the correct ports except for the last pipe. I get the message stating "Cannot connect systems with different fluids". I have also tried to disconnect the power, remove all products, and delete the fluids from the system.

The only way to alleviate this is to delete all buildings in the loop, leaving the pipes in place. Once all the buildings are deleted, I can connect the last pipe. Replacing the entities after all the pipes are in place does not generate the error message. I have a blueprint created and can send it upon request.

Most probable thing is that you have adjacent purifiers. The arrow in the building are all pointing out suggesting the connection is output only, but those are also an input.

Since purifiers output dirty water on one side and take clean water from the other, if you place them touching the dirty water enters the system where only clean water should be.

Try to leave at least a tile of space in between.

If you have robots/nanobots they can put down pipes for you. Skipping past the error of mixing liquids in pipes in this case.