Heat stick question

[STL_Lucas]

So I finished my heat stick and covered it with some DAP food safe silicone to be safe, definitely helped dramatically in how fast I could heat 7 gallons of water in my 10 gallon kettle on the electric stove, 56*F to 208*F in about 80 min. Problem is it topped out at 208-210 and wouldn't boil...

My question though is I tested this in clean water, it ran for about 100 min and I just unplugged and let it cool down in the water for several hours. When I pulled it out it looked like this.

Any thoughts on why it looks like this and if this would hurt anything?

 

[wilserbrewer]

I believe that is mineral deposit from your water.
Not a concern, just clean after use.

 

[STL_Lucas]

Thanks! Just couldn't believe how quickly that happened, any risk of cleaning with pbw? I know it's not like copper just wanted to make sure.

 

[MaxStout]

Vinegar should take off that mineral scale.

 

[wilserbrewer]

I use a green scrubby pad to clean elements after a brew, only takes a few seconds.