What is this stuff and what does it mean?

[Gideyon]

 

Anyone know what is building up on my suction cups and airline tube? 

 

I originally thought it was dirt.  But looking closely it's something else. 

Any thoughts? 

 

There are no organics in the tank. No fish.  Just substrate, 2 stones, and some crushed coral.

 

[Biotope Biologist]

Appears to be lime or mineral scale on the cord Pretty common if you have high gh or high kh.

On the suction cup that appears to be algae but if its hard and crusty it might also be lime or mineral scale.

[Gideyon]

Never heard of that before. Thanks! 

I had been dosing with baking soda because my KH was crashing due to the substrate. That finally settled.  But I guess this is the byproduct.